Nyx isn't the only frame that needs this, but as I'm the weirdo with about 35% of my 3.7k hours in Warframe played as Nyx, I'm massively biased and have my priorities lol
Yes, Terminator Nyx will still absolutely function, but I primarily use her 4 for cases of "nuts, got an (insert heavy unit title), pop my four and deal with it before moving on," and I prefer a more active playstyle utilizing her 2 and 3. I want her to work decently both inside and outside her 4. The following suggestions are meant to be touch-ups, rather than ability replacements:
First ability: Nyx could get more benefit out of actually using her first ability by implementing dual-casting for other abilities. For instance, her 3 could cover more ground with two instances cast, one by Nyx and a simultaneous one by her 1 target. This could prove very useful for her 2 (though I'd understand toning it down, the shield and armor strip will undoubtedly be quite useful in Steel Path), and could work for memes for lower levels with her 4.
Second ability: Leave as is, perfect match for Steel Path.
Third ability: I know what you were going for with Nyx's 3 + 2, but standard clunkiness aside, that ain't gonna cut it if we're dealing with level 140 enemies with double health. So a way to let us push that a bit further and make a bit more use out of absorbed damage would be (coding permitting) to allow Nyx to grant a debuff to enemies under the effects of her 3 based on the damage currently absorbed by her 4. Allow her to cast her 3rd ability inside her 4 regardless of augment, and open enemies up to more damage from each other (or have them deal more damage to each other, whichever is easier to implement) based on the amount of damage absorbed by Nyx before casting her 3. So, order of events: Nyx casts her 4, enemies shoot Nyx's 4, Nyx casts her 3, damage currently absorbed by Nyx's 4 transferred to the enemies in the form of either them dealing more damage to each other or taking more damage from each other based on how much she absorbed.
Fourth ability: See above synergies. Additionally, I'd recommend either increasing the base duration of the damage buff Nyx receives or keeping it active after Nyx recasts her 4. Also, would be fun if the buff gets shared with her 1 target.