While I don't agree that they are going to bring out an upgraded Wii with a faster processor (what good is that faster processor, games will still have to support the older Wii's) they could potentially have a motherboard upgrade similar to XBox360 and Sony do, primarily for the lower heat and thus lower cost required to produce the unit.
Video streaming and such as an upgrade, again is just a software upgrade.
Personally i think they will be expanding in the arena of new peripherals (Wii Fit, Guitar Hero, Rock Band) have demonstrated users will pay for them, and it is a relatively untapped market. Hell, some company is releasing a unit which lets you control aspects of a game through a fricken thought helmet.
Aside from that, the DS is probably up next for some sort of new design to come out.
Lastly, if anyone thinks Nintendo is NOT already working on their next gen console than they are being naive. The next gen Wii was probably started (at least from the conceptional point) last year. Just like the XBox3 is in the works, and just like the PS4 is in the works.