I won't bother with specs but more powerful, HD, '3D ready' more internal storage and much improved online are all musts. Unified friendcode.
Enhanced motion controls - WM (without constant recalibration) on both wii2mote and nunchuk. Sure add camera. Add an embedded analog stick to the wiimote (similar to the one on the 3DS). Better mic.
Backwards compatible with Wii, but I can't see GC. Why bother with adding the controller and memory card ports? It's becoming harder and harder to find GC games as it is. Move GC to VC.
Channels are fine but much more streamlined and 'push' material to users (especially casuals), especially WW,VC, Demos, etc. I'm amazed how many people don't even know about Wiiware/VC and especially demos.
Maybe do a simplified, Nintendo style, mii-ifed version of Sony's Home in the Mii Channel.
More ingrained with social media. Connect to Facebook/Youtube/etc. IE: Post game achievements to Facebook, SSBBrawl2 fights to Youtube - direct from games. This could potentially go much further.
The real question is what will be the new twist Nintendo adds? DS had touch screen, Wii had motion controls, 3DS has 3D. So what will Wii2 bring to make it revolutionary and more accessible? Beats me.
