Of course, the villain could turn out to be a major surprise, someone we didn’t expect at all – and there is certainly a lot of potential for that in both the universes of Batman as well as Superman. They are rich enough in different characters that the writers could create something really explosive for the fans to watch.
It could even be a more obscure, minor villain character that hasn’t been enjoying so much prominence on the screen so far. That would also be an interesting strategy for the writers, although it might be a bit of a disappointment for some fans.
After all, people want to see a massive, spectacular fight, and using a minor villain that’s not very popular in the community might be counterproductive to that. Or it could serve to boost that villain’s profile – we have no idea.
In any case, the film is getting closer and closer, and fans are soon going to see the epic fight go down. This film could easily set some interesting trends for the futures of both franchises – it would indeed be exciting to see Batman crossing over with Superman from time to time, although of course it might also start to get cheesy and worn out at some point if the producers do it too much. But for the time being, the idea is still original and fresh.