Oh sweet, a post requesting old warframes be changed/reworked! I have a few ideas myself.
Loki:
Loki is SUPPOSED to be a trickster god, yet his tools do not support this fantasy in current warframe. Here are my ideas:
Passive:
-Ontop of current ability, add the ability to reset nearby enemy's Alert/Awareness state to Un-alerted within a 10 meter radius upon killing with a finisher.
Decoy:
-Make clone immune to damage, only ending by its duration ending or it being nullified by respective sources.
-Greatly increase Decoy's threat level, so that enemies target it more frequently.
-For Savior Decoy, when Savior Decoy activates, grant an extra +5s (unmoddable) seconds of Invisibility.
Invisibility:
-Merge Hushed Invisibility into the base ability, replace with a new augment; here are a couple of ideas.
-While Invisible, Decoy becomes capable of stealing Eximus Auras from nearby Eximus, and casting them on a certain cooldown centered on the Decoy.
-While Invisible, hits on the Decoy activate On-Damaged effects for Loki such as Arcane Avenger, or Arcane Aegis, as well as disarm enemies in a small unmoddable 6 meter radius around the Decoy.
-While Invisible, Grant Status Immunity
Switch Teleport:
Honestly, This ability is largely unsalvage-able and pretty much useless. Just replace it. You did that with Undertow on Hydroid, and look where that got us? Hydroid's great now. Switch teleport is not.
Radial Disarm:
-Merge Irradiating Disarm into the ability itself, replace augment with something new; here are some ideas.
-Allow this ability to disable Enemy abilities such as Eximus Auras or Acolyte abilities for its duration.
-Allies within the cast radius of Radial Disarm get A fraction of Invisibility's Duration, including the Status Immunity from Invisibility's theoretical augment.
-Grant a 50% Armor strip, scaling with power strength up to 100% with 220% power strength.
NOTE: With the "replace X augment with something new" parts, I am suggesting that ONE of these be chosen for a new augment idea. Not all of them. That would be silly.