Yes, that would actually sound great. It's the mash-up of different games that would interest gamers, and a racing game like that would definitely be a hit with gamers from all ages and generations. It needs to be incredibly balanced though, as people would just keep using their favorites, and it won't be as fun as trying them all out one at a time. Maybe someday it will be a possibility and now we just wait for them to release it.
I think a smash bros approach to this series would be fantastic. It would be so cool to race against sonic and eggman, which is something we have never been able to do before.
That seems like a cool idea, and probably the game would be fun, but it seems a lot like Super Smash Bros: Kart Edition. Still, can't deny it, I would play it for sure.
I'd love to see these characters finally cross over and combine with the Nintendo characters. I think this would be the perfect game to do it with too as well as smash brothers as you've mentioned.
You know, now that you mention it, it is kind of one of the why not issues. It makes me really wonder why they have introduced these other characters in Smash Brothers but not other games that it could be used in, like Mario Kart. I think it would be awesome and I would certainly pick it up, and I am sure that everyone else who likes the game would too. They should think about it, because it would certainly make some real money.