I'll buy a Revolution for the next Smash Bros and Zelda, but it's not coming out for quite a while, so I'm not really thinking about it right now. Also, I've got a feeling the "downloadable content" from past Nintendo systems will only be first-party games. But I could be wrong.
And, lastly, the XBox 360 will run an emulator to play regular Xbox games. Microsoft has said it won't be compatible with everything, but it'll definitely play "Hot Titles."