I think either Cyrax or Sektor would be awesome, think of the customization! They could really go crazy with all their alts and stuff.
Buuuuuuuuuuuuuut, they're both in the game with their MKX movesets so I think its extremely unlikely they'll make it to MK11. NRS wouldn't just plop them in with MKX movesets because that would be lame as fuck, and NRS redesigning the moveset of a NPC before adding them has never been done before. And to me Robocop getting their colors and special moves similar to them is the final nail in the coffin. I would love to be wrong.
Realistically I think Havik is very likely, and any ninja esq character is very unlikely (sadly). So my vote is for Reiko or Hotaru cuz this is probably their best shot of ever making an MK game again. How to stretch those characters across multiple variation beats me, Reiko can only throw so many stars and spin so many ways, but I trust NRS to make them cool.