Fortuna and PoE are a great addition to Warframe, and clearly the first steps towards DE's future approach to level design and world-building. I have suggestions for how to improve both areas with features that will allow for more enjoyable and immersive open-world experiences. The recent rework did a lot to make the plains prettier and update the economy and mission mechanics, but when I play Orb Vallis and the Plains, neither feels immersive or "living" enough. Whenever I play on these maps, some part of me longs to have more reasons to explore the landscape and interact with these beautiful environments. What I suggest would take a lot of development time and resources, but these open world areas justify the investment, as they are the next and newest iteration of Warframe- this type of content is what Warframe is heading towards. As such, these areas should be as awe-inspiring, interactive, dynamic, and enjoyable as possible within reason. I'm not a performance expert, so it's possible that some of these suggestions simply aren't viable from a performance standpoint, but I tried to not suggest simply making things prettier and more processor-intensive, that isn't really the goal anyway.
Fishing: Fishing can be enjoyable in short stints when you get lucky and get a bunch of rare fish, but most of the time it strikes me as tedious. I suggest something more exciting and interactive. Players should be able to jump into any body of water and swim around with their fishing spear. Just as players cannot shoot fish with their weapons, they would only be able to catch fish with their fishing spear and/or possible new options like chasing fish and catching them with nets. Archwing wouldn't be necessary to swim underwater, as this would better integrate this new mechanic into the game. Allowing players to fish in/under the water would allow for more interaction with the environment, and add more diversity to what players can experience on each map. Furthermore, this new type of fishing would allow for larger fish and the possibility of aggressive fish that the player would have to play "matador" with, as well as environmental hazards that could correspond to more lucrative fishing areas. There could also be underwater caves that connect to the existing cave networks. Obviously this feature would require a bit of work to implement, probably including a re-fit of most bodies of water to be much more detailed/full of plant life. Ideally, players would start to swim whenever they entered water to a level that, before, would re-spawn them on land, making the mechanic pretty seamless. Very small bodies of water that are barely deep enough to accommodate the player would not need much detail, but could still spawn small fish, or these smaller ponds could be remade to be deeper or wider, or areas that are too small to support swimming in a robust way could allow players to float, but not dive under. The coastline of PoE could be retrofitted for a larger ocean-like coast environment and feature some of the largest plants and aggressive fish types. Perhaps these larger fish could even drop parts to other smaller fish when caught or killed. The grineer wind-farms could be build out on both coastlines to add more solid structures above the water. Underwater environments could have collectible resources and plants to further encourage players to swim around and add more interactive elements to the environment.
Fauna: In order to make these places feel more "alive" with real ecosystems, the animals that live in these places should spawn in the open, instead of being "hidden" for conservation purposes. Interactions between creatures should be established, such as Sawgaws and Verminks hunting Pobbers, and Stovers and Kubrodons fighting among themselves and attacking essentially any other creature for food. In order to make conservation still work in the way it does, the common form of each creature could spawn readily in the wild, while players would have to hunt for the rarer two just as they do now. This would be justified because the "rarer" variants of each species would be endangered while the common versions could be given a ecologically stable status. There could be Sawgaw nests, perched high up in the bluffs or on top of mushroom clusters, Pobber dens at the bases of mushrooms, and Kubrodon dens in sheltered areas near coolant reservoirs. Pobbers could be found eating small interactive mushrooms for food and water. For the PoE specifically, Feral Kubrows should be added with updated Kubrow dens that don't look so silly, and are integrated into the terrain as opposed to mounds that have been randomly placed on flat ground. Fast prey animals that run around the plains should be added for kubrows to hunt. Condrocs could be found near the carcasses of dead prey animals, and circling Kubrow packs to take left over scraps. Mergoo's could be found hunting for Kuakas in the forests. A prairie-dog sized animal could be added simply for more diversity to fill out the ecosystem. Kuaka burrows could be dug up for a chance of unearthing gems, and Mergoo nests near the coast could be plundered for fish parts. Such changes would make the ecosystems present in both maps feel much more alive, as opposed to just decoration for the eye. Wildlife could be killed with normal weapons, and possibly even yield drops, but conservation would present a much more viable way to get the same resources so that players still have an incentive to conserve instead of kill.
Terrain: With an amazing parkour system, our open world areas suffer from being too open. While Fortuna is better than the plains in this regard, the landscape could have much more presence and promote more interactive mobility if more vertical terrain and multi-level environments requiring vertical traversal were added. The following suggestions focus on adding more vertical aspects to the landscapes as well as more vibrant environments for the ecosystem suggestions earlier: What we currently have in the Orb Vallis are looming mushroom canopies that lack ground-level detail or density. Mushroom forests should have different sizes/ages of mushrooms and taller patches of grass, that create a sort of underbrush/cover for wildlife. Such a change would also allow for better stealth and mobility opportunities for Warframes with the smaller sized mushrooms functioning as cover and stepping stones for better access to the tops of the tallest mushrooms. These mushroom forest patches/biome areas should be expanded so that most of them are connected, giving these areas a more present and expansive feel. This would also give the wildlife a more realistic way of moving around.The forest areas in the plains should be expanded to surround lake Gara Toht and extend all the way up the banks of the stream that feeds into the lake. Honestly, the forest areas should just be expanded in general; there are a lot of areas that still look very bare, even excluding areas that are reserved as actual plains, such as the giant slope between Gara Toht lake and the Grineer Radar Base. Large-branched trees should be added as perches for both types of bird in the plains. Both areas should be given elevated small-plateau areas that feature wildlife or small outposts of enemies in areas that are already very vertical/elevated in order to create more content in vertical areas; as of now, Fortuna has some very steep environments, but there is often very little there, and thus no reason to go there.
Caves: This section is sort of an expansion of the terrain section. The cave networks on both maps should be heavily expanded on. At the moment, both of Warframe's open world areas are wasting the potential of underground content. Underwater tunnels could connect bodies of water to cave networks, which should be interconnected enough to allow for underground player travel between many parts of the map. These networks would serve as an extension of, and connection between, animal habitat and forest areas. The cave networks would add another level of verticality to the Orb Vallis and the PoE, and would feature pristine areas with higher concentrations of underground creatures and plants (extending animal habitats and connecting forests), as well as areas occupied with Grineer or Corpus activity, equipment, and enemies. Rare grineer and corpus caches and/or enemies that protect the caches could be randomly distributed in the Grineer/Corpus occupied areas of the cave networks each game, as well as cave-specific collectible plant resources. On both maps, most of the larger enemy outposts should be expanded to underground facilities that connect to the cave networks on their deepest and most secluded levels. These facilities could randomly feature spy, sabotage, capture, and rescue mission opportunities/dynamic alerts which would reward successful stealthy approaches (if enemies turn on alarms anywhere in the facility, the rescue-target kill timer will start, the spy vaults will get harder or yield less valuable data, the capture target will start an escape route, the sabotage will result in less rewards or a timer) and as a result would perhaps be easier if infiltrated from the cave networks. Such a feature would give these bases more interactive purpose as well. In the case of Orb Vallis, caves could have underground freshwater ponds and running water to better justify how the animals stay alive (servofish would still spawn, but perhaps an organic fish could be added to the caves as well). There could be mining sabotage/excavation missions in the actual cave networks, which would yield varying amounts of gems as a more gem-focused alternative to killing Thumpers and Orbs.
Orokin: In both areas, the ruins of the Orokin should be expanded. There should be more Orokin pillar ruins in the plains and the larger ones should have entrances near the tops that allow players to traverse up to them, and enter. The Orokin coolant tower in the Orb Vallis should also feature an interior, and there should be more orokin structures littered across the Vallis map. These interiors would lead to underground chambers that would tie into the larger underground networks talked about in the previous section. Players could hunt down underground Grineer/Corpus expedition parties in the cave networks (each expedition would have a leader who would try to escape) to gather the parts for an Orokin key which would allow players to activate a specific dormant orokin gate of a few that are located in the cave networks. Doing so would open a portal to a pristine part of the void. These void-facilities could feature puzzles like Lua, and/or Orokin vaults like those in the derelicts. The rewards could be mods, prime relics, endo, and/or Ayatan sculptures, or could tie into the local reputation systems, whatever DE sees most fit. Ideally, some rewards that players want to simply get, and some rewards that players can never get enough of. The rewards should vary between the two maps to give players reasons to do both. Such a feature would give the Orokin ruins already present in both maps more meaning, and add another interactive task for players that offers more environmental diversity (the void).
Presence: Both areas would greatly benefit from an increased presence of both enemy and allied factions. For Vallis more Solaris and Corpus activity, and for the Plains more Ostrons and Grineer movement. The Ostrons could have small outposts for relaying intelligence about the grineer, as well as serving as bases of operation for salvaging expeditions to Orokin ruins and crashed Grineer ships. These outposts would be pretty well isolated and low-profile, but at times they could be beset by Grineer assaults or ghouls, allowing players to defend them during dynamic alerts for a small reward (perhaps minerals or fish or both). Players could start bounties from these outposts so long as the outposts were defended, and perhaps the outposts could offer limited-time conservation missions that are more involved and give more standing, requiring players to fend off the enemy, the context being something like: the scouts report a rare (animal) was spotted at (location), being threatened by nearby enemy patrols, go there and save it. As for the Grineer, they should have cargo ships flying between outposts (adds more vertical activity) that could possibly be boarded and hijacked (and possibly brought to the Ostron outposts) for certain rewards, or simply shot down for little reward. To add more interactivity between the two groups, there could be Ostron salvage expeditions that go to crashed Grineer ships or orokin ruins, again offering dynamic alerts in which players must defend the Ostrons from surprise ghoul attacks. In the long run a feature that possibly involves large Grineer airships/bases defended by flying and mounted Grineer would add more vertical content, giving players something to actually use their archwings against. In Fortuna, very similar ideas could be implemented.
TLDR: I suggest a lot of feature that would improve player interaction with the open-world environments, give players reasons to explore and enjoy these environments, ramp up the immersive-ness by creating more vibrant ecosystems, and add to the verticality and vertical content of the maps to better mesh with Warframe's mobility system, and simply to add more content and, again "immersive-ness".