I think it will happen this gen, because I don't see their next console doing something that will add much value to SMB. They may as well make a Wii version with it's massive installed base, especially if the next console has backwards compatibility.
Beyond that, I think the Wii has many more years left in it, there's plenty of time to release a sequel without cutting the original too short.
A game I'm developing with some friends:
www.xnagg.com/zombieasteroids/publish.htm
It is largely a technical exercise but feedback is appreciated.