Alright, so now we know what pattern Ultimates followe - they are mix of existing special moves with a little spice in form of brand new animation.
So knowing what we can expect, lets post our suggestions for future Ultimates. Mine go like this:
Spinal: Lock enemy in bone prison and do nothing, just leave him like this to die. OR, modify his throw animation to crush opponent bones like Shinnok does in MK4 and MKX
Orchid: call Firecat to bite enemy to death, similarly like Riptor does in his win animation.
Gargos: do some hand gestures, purple FX surround enemy and turn him into a mimic.
Fulgore: Fulgore calls in bunch other Fulgore units that obliterate opponent with crossfire of Hyper Beams.
Glacius: Freeze up enemy and shatter him, or make him drown into ice puddle like in classic KI.
Rash: summon speedbike, put frightened enemy on it and make it go off, and we can see multiple blinking wall obstruction alerts like in infamous NES levels. Make it suggestive (or put a bike crashing noise few seconds later, watching Rash stupid grin in meantime).
Cinder: put off his mask, white flash of nuclear energy occurs and after that we see Cinder in victory pose and skeleton of opponent.
Eyedol: he performs his infamous bull stomp with recreated sound effect, charges at opponent and performs his forward throw with added sound effects and/or looped animation, to make it look more brutal.
Sabrewulf: perform his lunge into his win animation but actually ripping on enemy instead of floor. I could not come out with anything fancy for him tbh. (potential candidate to not have ultimate?)
Sadira: wrap opponent in web and hang upside down, similarly to how some dude is hung on right side of her stage.
Kan Ra: use animations from Eyedol trailer, mix them with his win “soul-steal” animation but we see victim, and make him say something like “I grow stronger” or “Yess, more power!”.
Mira: scare opponent with herd of bats, then camera switches to first person view of victim, vision covered by bats, suddnly Mira approaches and bites his neck, lethally this time.
Kilgore: self destruct into opponent face with Predator-like sounds or sinister beeps.
Kim Wu: Liu Kang MK4 dragon fatality, OR Shao Kahn death in MK9 story mode (would be more real to be developed).
All I have for now.