The thing is, that when they made the Mario and Sonic Olympics games, they didn't replace anything. If Mario and Sonic Racing get's released this christmas do you believe tht Nintendo will make a Mario Kart for the same Christmas/next year? I think they will make one of them, and this is where my question in the OP comes in.
I say this is enough. why make another one? Just add in Sonic characters and locations and call it a day.