...Well I guess this is just going to sit here I can answer.
I do have a sneaking suspicion that there are more characters in the roster this time, mainly because of how the footage handled its flags. As to who I think the additions would be;
-Rouge is almost a shoo-in, being the most prominent non-playable mainstays of the series.
-Espio I think has a good chance, if only because Mario and Sonic Rio was all too keen to group him with Vector (I'm serious; the character profile page had nine per line for a ten person roster, and Sonic's side made Vector the tenth slot and the first slot of the one-event roster went to Espio, Despite DK also being made tenth slot, Diddy Kong didn't get the same luxury).
-Everyone else I couldn't guess, but I'd say Cream, Jet and Eggman Nega have less chance despite their seniority. I'd say Zavok too...but TSR kinda threw that idea out.