The characters that probably have the highest chances of being cut are Scorpion, Bane and Zod. Guest characters usually don't return in sequels. Bane was really only in because of TDKR. And similarly Zod was really only in because of MOS and after that has had little relevance. Initially I thought Batgirl, Killer Frost, Grundy and Ares had high chances of being cut as well, but now it's probably 50/50 with them since fighting games based on licensed franchises have the tendency of promoting new or upcoming materials, Batgirl will be in the upcoming Killing Joke animated movie. Killer Frost is apart of the Arrowverse. Grundy is confirmed to show up in Gotham's third season. And Ares is rumored to be the villain in the Wonder Woman movie.
Newcomers I would like and expect to show up would be Black Canary, Supergirl, Vixen, a couple of characters from Suicide Squad(preferably Killer Croc and Captain Boomerang), Black Manta and Captain Cold.