Why would they need to release a Wii 2 right now? Sales of the original Wii are still doing fine.
Hardcore gamers have been against the Wii from day 1, and now that it's so massively successful, they are eager to see it replaced as quickly as possible.
From a developers perspective, the extra cost and resources of developing Wii HD games just wouldn't make sense, especially when it's so close to the launch of the 3DS. I'm sure Nintendo is counting on the 3DS and Wii to share content now that they have similar processing power. For instance, we've heard of Epic Mickey and Goldeneye coming to the 3DS, and in the same respect games made for the 3DS can come to the Wii with little to no optimization.
The only thing Nintendo needs to do is keep the Wii experience fresh by releasing new, compelling software.
