Let's face it - the abilities to become totally untouchable and to fully freeze all enemies for practically ever were always brittle ideas - there's just no way for them to exist without being overpowered (and worse, uninteractively overpowered) or useless, and the current behavior of overguard has that pendulum on "useless". So I've cooked up some ideas to bring Limbo back into warframe, and hopefully leave him in a state that is:
1. Capable of engaging with the game in an active capacity
2. Still faithful to the power fantasy of being the nigh-omnipotent god of your own plane
3. Given a spread of abilities that can be balanced in states other than "AFK" or "Useless"
4. Less frustrating for allies to engage with.
The Rift
The rift no longer grants total damage immunity. Instead, units in and outside the rift mutually do 20% damage to each other. Ally damage is then multiplied by limbo's power strength (only if it is positive) and enemy damage is divided by it. So, for example, if Limbo has 300% power strength, then allies deal 60% damage across planes, while enemies deal only 6.66%. In addition, Overguard no longer grants immunity to interplanar damage rules.
Taken in conjunction with other survivability tools (more on those later) this should allow a limbo who wants to just use Limbo's rift as a safety zone the ability to do so - as long as they're willing to invest in that.
Temporal Manipulation
Limbo's 2 becomes a tap-hold. Tapping casts Stasis as normal, but holding instead allows Limbo to selectively Accelerate the flow of time, amplifying ally health/shield regen rates, reducing their shield regen delay, and increasing projectile speed. Meanwhile, enemies suffer increased status tick rates.
The goal is to enable limbo with an option that's suited for active gameplay - something which allows Limbo to confront un-stasis'd (and un-stasis-able enemies without feeling afraid for his life.
Cataclysm
Base size reduced by 25%. No longer shrinks over time. No longer "pops" on contact with a Nullifier field, instead shrinking over time while in contact with one. Slowly re-expands to normal size once the nullifier field is gone.
New Augment - Cataclysmic Heart: Cataclysm gains a hold-cast. When activated in this way, the cataclysm is now centered on Limbo and moves with him.
I'm working a little out of order here, but this is important for context. Currently, Rift Surge is primarily used as a way to deal with the fact that enemies will keep entering and re-leaving cataclysm as it shrinks. While rift surge is theoretically usable as a way to selectively bring enemies into the rift, and to pull them in without leaving, but this is a bit slow for modern warframe. I think it's worthwhile to replace the ability altogether, and modifying cataclysm's behavior is a part of setting that up.
The augment, as with the rest of the changes, is designed to enable a "combat limbo" style of play - a Limbo who's actually useful outside of stationary defensive play, who can efficiently keep up during even an exterminate rush.
(Also, it's always annoying to me that dashing forces me to leave the rift in common play as Limbo, so this is a way to maintain mobility without having to deal with that)
New 3rd Ability: Physics Flux
Limbo adjusts the laws of friction and gravity within the rift for a duration, causing enemies to miss a percentage of their shots while granting allies increased parkour and slide speed.
A relatively simple skill to aid in survivability, make cooperation with a Limbo feel more natural, and allow players to keep up with the rate of play they're used to without feeling compelled to dodge-roll out of the rift for mobility's sake. This also hopefully adds to the idea of "master of the rift" by adding more that the rift can do than just play with time.
Thank you for reading. Please let me know any feedback you have - obviously, any idea will be rough around the edges, but I hope that at least the core of these is sound enough to inspire the idea that Limbo can be more than the "necessary evil" of defense and excavation missions - that he might be able to fulfill his old defensive roles, and the fantasy of Limbo, and be valued as an enjoyable supporting presence on the team.