Actually I think you got it backwards there. Sonic was first sent to the game cube, and then some later games were realeased for all three systems at the time. Sega is basically part of nintendo now, making some games for other systems but saving the rest for for the WII now.Sonic was originally from Sega, then it was passed to XBox though some versions were playable in Nintendo Consoles. .
And on that, I think the guy from Knights would be interesting to have in another SSB game. I could imaging what some of his abilities would be