Here's an interesting article:
Basically, it's an anayst stating that we may see a Hi-Def Wii in 2010, and that the next generation of systems likely won't happen until 2013.
I hope he is right. Honestly, having the new crop of systems coming out roughly every 5 years is really getting old and pricey, especially with how much the systems cost this last time around compared to the previous generation.
Plus, I think we aren't that far off from the graphics getting so good that there won't be much more room for improvement.
And with the loss these companies are taking on these systems in most cases, the longer they are around, the better off they will be.