I can almost guarantee you that the next Wii console will be in "HD". Nowadays, "HD" isn't that big of deal. Most people are buying "HD" televisions and all "HD" graphics require is a bit more powerful graphics processing. By the time the new Wii comes out, "HD" will be cheaper and thrown on as an afterthought, just like the progressive scanning for 480p they put on the Wii.
Now, I'm not saying that will be the selling point of the new Wii. I'm sure Nintendo will come out with something new and impressive. I'm just saying that making the console "HD" won't be a big deal then.
edit: I should learn to read the OP better before I post :P