I think Nintendo should (and will) wait to launch a follow-up console until at least 2012, because they are still rolling out a lot of big properties for the Wii (as mentioned ad nauseum with the Mario/Zelda/Metroid trifecta), and usually there's a couple years' gap between releases in such key franchises, you'd expect that they'd have at least one (or more) of those ready for launch with a new console. Plus the Vitality Sensor, which while I have no idea (none of us do, really) how that will do for N, seems to be their focus now, and I can see them playing that up for a good year to year-and-a-half. Maybe late 2011, but I'm thinking 2012.
Bah!