I'm with Mademan. For the longest time I was all for a Sonic & SEGA All-Stars Fighters, but after thinking a bit I realized that Sumo might not be up to the task of making a competent fighter with a large roster and varied number of arenas. Designing a fighting game just isn't in their area of specialties, however they totally excel in designing Tennis and Racing games. Unless they co-develop a fighting game with AM2, which would rule, I say they develop Sonic & SEGA All-Stars Racing 2.
Here's what they should do:
• carry over the complete character roster from the first game
• add about 10-15 more characters, focus more on classic SEGA racers (Hornet, Hang-On bike, OutRun car) and add the often requested characters from the first game: NiGHTS, Ristar, Vyse, Panzer Dragoon, PSO, Shinobi, etc.
• offer up a DLC racer/track pack (with 4 racers and at least 3 more tracks), maybe have THIS be the AM2 racers. People would buy the hell out of this DLC.
• all new tracks! maybe revisit IPs from the first game, but only have one track per returning IP (with the exception of Sonic, however the new Sonic tracks should be areas from the Genesis era like the Death Egg DLC of the first game)
• new tracks should be from a broader range of IPs. Space Channel 5, NiGHTS, Phantasy Star, Shenmue, Jet Set Radio (first game), Alex Kidd, Fantasy Zone, OutRun, Hang-On, Daytona (or SEGA Racing Classic)
Hell, even if they just add 8 new racers plus a few more via DLC, and spend more time on developing a broader range of tracks, I'd be all for it!