This thread is full of win!
Panzer Dragoon fighters duking it out against Jet Set Radio punks would be so awesome! Lets not forget Outrun-style stages, and a Soft Museum stage too! As you can see, I've actually thought of this before, its a neat idea.
Skies of Arcadia, Shenmue, Yakuza, JSR, Panzer Dragoon, Nights, Ristar, Outrun, After Burner, Burning Rangers, Golden Axe, Virtua Fighter, Samba, SEGA Rally, Phantasy Star, Shining Force, Streets of Rage, and Sonic of course. So many great Sega memories, I'm probably forgetting some though...
You have no idea how happy this would make me, but I'm pretty sure they wouldn't blatantly copy something like this. Oh well, Superstars Tennis will have to do.