here are some moves that i think should return in mk6:

Raiden's teleport
reptile's invisibilty
scorpion's leg grab from mk2
sub zero's slide
kano's grab and bite(think about it,in 3D)
shang tsung's transform
jonny cage's nut punch
sonya's square wave
jax's wave projectile

those are just a few moves that i think should return