Now I'm not denying Nintendo is working on a new system, since I've stated before that I know companies always are. I'm just not buying any of the details in the rumors, and this thread shows that while Nintendo likely has something contrete now, any of the details are really not something to buy.
So while I'll give, as I have before, that at least an announcement of another system is likely at E3 or later (like Tokyo Game show, PAX, or one of Nintendo's own conferences), I would say more Motion Plus games will be shown than any full blown system announcement. Why? Because Nintendo barely scratched the surface of that, and while Sony and Microsoft showed they were just playing catch-up to the Wii with their controllers*, Nintendo can show they can still make better games.
They aren't going to just let the Wii coast along until the next system is released. That isn't practical at all. Not unless the new system was coming out no later than this holiday season, and I haven't seen anyone here entertain something that ridiculous.
Nintendo needs to keep the momentum for the Wii going, not just to fund R&D on the next system and its games, but to keep Nintendo on its toes, and to keep the audience there.
Just because the gaming community wants the Wii to go away doesn't mean Nintendo is going to do that, nor that the mainstream is clamoring for another system based solely on greater specs. They want awesome games (CoD is sells for being awesome, not for being HD), and Nintendo is going to keep delivering that, even on the Wii, so that when the next system comes along, people will see that awesomeness and continue.
* No, Nintendo would not be playing catch-up with a more powerful system. They would just be doing what is finally affordable, since they know they could lose billions otherwise.
A flashy-first game is awesome when it comes out. A great-first game is awesome forever.
Plus, just for the hell of it: Kelly Brook at the 2008 BAFTAs