Well, if we take the REAL Car Soccer World Cup to be a part of motorsport...
I accidentally managed to watch the finals of the one in Germany, don't know when it was, maybe last year? VW Polos against a huge ball in a stadium. It was fun to watch. Can't remember who won though
If they make it like that, so the ball is really a ball and not a car, and there's a proper stadium for that at least, no problem at all.
About the bowling thing: I don't know. But why not include it?
Tbh I'm a bit bored with racing games always using the same tracks, same modes, same cars. Forza 4 seems to be a game with realistic physics, and a good game overall, and I'm happy that they think about other "sports" than just racing. Definitely a +.
Edit: Just found it, it was "Autoball Weltmeisterschaft", and yes, it was in 2010 in Cologne
They were only 1 on 1, so 8 vs 8 is different, but with a properly sized track it should be no problem.