I meant the general idea. I own Sega All-Stars Racing, so I know what you're talking about. If you ask me, they put TOO many characters from Sonic in there...I mean...Big the Cat?
However. To clarify what I meant, I'd include: Mario, Luigi, Peach, and Bowser,that's about it. You're right, Yoshi and Wario would probably be included because they have their own games, but NO WaLuigi, or any characters from those games other than those two. I'd include Donkey and Diddy Kong. And then from there, probably Kirby, Meta Knight, King Dedede, Link, Zelda, Gannon (the original version, not GannonDORF, just for fun), Samus, Ridley (a smaller version of him, so as not to be ridiculous), Pit from Kid Icarus, Captain Falcon from F-Zero, Ness from Earthbound, etc.
I'd probably include a few more obscure characters for fun, like the dude from Mach Rider, Mike from Startropics, Little Mac from Punch Out, Starfy, stuff like that, to fill out the roster. But the MOST important thing, would be to have some fantastic, fully fleshed out tracks that actually resemble the game worlds the characters are from.
On a different note, I really like my Star Fox idea, what with choosing to play Fox or Wolf and all. Too bad it likely will never happen.