Well, we know it isn't DLC-related or UMK9-related.
It isn't MK10 or MK vs DC 2, either.
And one of the surprises is a GOTY edition, I'm certain of it.
NRS had a job opening on their website asking for people skilled in the action genre, so we've speculated that one of the surprises could be a new action-adventure game.
And it's also been speculated that an MK character could be a DLC character for Batman: Arkham City.