A forbes interview with Reggie Fils-Aime:

“The way we approach that innovation,” he said, referring to Nintendo’s innovative “jumps” (like the Wii), “because we have hardware developers working side by side with software developers, is that when the software developer comes forward with an idea that can’t be executed on the current platform, that’s when we start thinking seriously about the next system. We’re not there yet, from a Wii perspective.” Of course, E3 is still a few months away.

I normally do not believe anything when Nintendo talks about a next system. They have proven to deny something all the way up to the day it comes out. With that, I still believe we will hear something about the next system by the end of this year.