The DLC characters are almost certainly Batgirl, Zod, and Scorpion. Too much is pointing in that direction.
I highly doubt there will be more than the first four, they were "considering" more for Mortal Kombat too, didn't pan out, new console generation is coming within the year, people will be moving on, no way would they manage to keep up the hype that far into the future.
Boon is a notorious troll. It's what he does.
....
That all said, the three after Lobo are terrible, terrible, terrible choices.