Not Sonic characters cause the game is already loaded with them.

We need more of the best characters from your other franchises like:

NiGHTS, Reala and Jackle from NiGHTS into Dreams
Ulala, Pudding and Jaguar from Space Channel 5
Beat, Gum and Yoyo from JET SET RADIOOOOOO!!!
Billy Hatcher
Jacky & Akira from Virtua Fighter
Amigo from Samba de Amigo
Axel and BD Joe from Crazy Taxi
Joe Musashi from Shinobi
AiAi and MeeMee from Monkey Ball
Vyse and Aika from Skies of Arcadia
Ryo Hazuki and Lan-Di from Shenume
Alex Kidd
Ristar
VectorMan

And probably a whole bunch more that I forgot would make this roster go from great to insane. Not to mention the potential for race tracks that could be added for each character.

This kinda content would easily justify the price tag whether they're DLC or not and give the game some serious longevity.