the Wii is finally losing market share to the real consoles, and any ambitious sort of game development outside of Nintendo is particularly rare, and with the actual gaming machines copping Ninty's style, it makes sense that they'd want to tease something for the future, even if its very far off, just to not be behind the curve.
I believe, sorta. They want to drum up interest in their future efforts, they want to keep third party development from completely abandoning ship, they want to not be behind the now fully caught up competition. A reveal makes sense.