If you are interested in creative theorycrafting, or you're looking for inspiration, take a look at some concept of mine:
Status 2.0 Concept.
Assassination Mission Rework Concept:
An elaborate concept about giving Assassination Missions a new dynamic, interactive, challenging and entertaining look by mixing it to other mission type and handing the player the choice on how to face it.
Both Gun'nRun or Stealth'nParkour.
Defense Mission Rework Concept:
Brainstorm and Ideas. Turning the well known BORING Defense Mission into a Dynamic Fortress Defense.
Melee Overhaul Concept:
Giving melee a reasonable twist to make it suit better Warframe's lategame. Through 6 points concretely revolutionize Melee-only and making it valuable even late game.
Level Design Concept:
Reviewing the importance of traveling through the map's areas, exploration, lockers, ammos and secret areas.
About Stamina in PVP:
Adding back STAMINA as a limitation to the extreme unending mobility to support a Window of Opportunity/Power concept without taking away anything from players.
Nekros' Ideas and Augments:
Volt's Rework Concept:
Re-conceptualizing Overload inspired by Equinox's Metamorphosis to empower its other skills.
Sniper Brainstorm Ideas:
Fantasies about enhancing the Sniper's gameplay.
Concepts I Support:
Mag Overhaul by D20:
Mod System, interaction with Damage and Scaling by WiiConquered: