So Captain Marvel blows people out of the water but Cassie just gets left out for MKX?
I mean you're asking some hardcore fans here so of course Shinook and Ermac but Cassie has that non collector appeal.
Raiden with lights would be amazing (and no doubt difficult)
Shinook
Ermac
Kung Lao
and just to show support:
Scorpion MK9 Revisit
Ermac MK9
and a modern Shang Tsung would look great too.