Sorry for short OP, fiddling round on phone touchscreen with image was a pita but I put it down to crap phone more than anything. Hate typing on it for long stretches if I can avoid it. Might do collected characters and update periodically through thread than try and bash it out on phone, anyway...
Though the Lui Kang ending to MK11 showed him beginning to train The Great Kung Lou, I'm pretty sure that guy lived for millenia regardless, before originally falling to Goro. I don't see why he can't defeat Goro (Or Goro's dad in a character switch like Sub Zero getting cyberized in MK9, to allow Goro to still be playable later (although what is death in MK really?). I don't think MK12 has been expressly stated to take play in GKL's time period, has it?
From the MK1 roster, I'd give a heavy pass to Sonya and Kano. I've seen their story retold so many times. Even in most spinoff media. I did think at the end of MKX's inter-connecting story ladders that they'd put an end cap of Sonya/Kano finally, if not at least writing most out to leave to Jauqie's backstory, but no, MK11 had Jax, Sonya, Kano and younger versions all out in full force.
Besides that I don't think you can cut Lui Kang or Shang T'Sung or Raiden/Goro for what they represent to the story. Nor can you get rid of the two main Ninjas, or Reptile as perhaps the first secret fighting game character (?). Johnny Cage is more expendable, but I think you'd want the comic relief character to stick around.