They were zipping him up in a body bag at the end of Man of Steel. And, there was speculation that Lex Luthor would have experimented on his body, which resulted in Zod becoming Doomsday. Now, it seems the execs at Warner Bros. have been trying to keep the lid on that bit of news and been trying to have Michael Shannon not reveal anything more. First, it sounded like he was going to be in BvS, now it is the on permenant hold Man of Steel sequel. So, its up in the air at the moment.
Lot of the characters making appearances have been crossing over onto each show. It would be likely that having Green Lantern appear would mean he would also appear on Legends of Tomorrow. Aquaman seems like another likely choice to make an appearance. They could get Alan Ritchson to reprise the role, same with Elena Satine as Mira. Don't see why they can't have Wonder Woman appear either, or even Wonder Girl or Donna Troy. They're having Hawkman appear too.