I could see this going a number of ways. If they wanted to end the fighters' pass with a bang (after all this was at one point planned to be the end of DLC) Then I think Geno makes the most sense: Highly requested for a long time, retro rep from a popular game, thought to be impossible because of rights. I see him as being the "biggest deal" left out there in regards to smash gets.
However, it could just as easily be another Terry situation, a character certainly deserving, but one that folks weren't really considering due to relevancy or relationship to Nintendo or whatever.
Or, hope against hope, it could be our girl in all her half-genie glory. Her odds aren't as great as Geno's, but if all the leakers are on the money, she is one of the few left with a serious shot. Anyway just a few minutes away now so we will know soon.