I looked and there was no topic existing.
If there is, link to it.
Mods, feel free to change the title to something better.
I will begin with some features and examples of games.
HD
At least 720p(real 720p, not stretched 480p. 1080p prefered.
Enough power to run Brawl at 120 FPS.
You know, just in case LCD TV makers wanna take that leap past 60Hz.
Eye/Head/Body Tracking
From something standing off to the side, like IR/non-IR cameras
More Axis
3 Accelerometers AND 3 Rotational Sensors(X,Y,Z+Rotation,Yaw,Pitch)
Higher Bandwidth Comms for controllers
Enough for 12 of what Wii uses it for now(Wii Remote+WMplus+1), but also have the ability to allocate it to many simple(low BW) control schemes(casual fishing games) or 1/2 complex(high BW) control schemes(multi-controller setups for full body control)
More Input Methods
Microphones, maybe, meh?
Built in Ethernet port
Damnit, why not? sheesh!
Rechargeable Batteries
Replaceable Li-Ions
More Standards
USB(charging, mass media, wired controllers), DVD(the Wii can do it, I've watched Gran Torino about 3 times over LAN)
Sell 1st Party USB-x Adapters
x=NES,SNES,N64,GCN controllers(they'll print money)
SDHC HW/eSATA/SMB Support
Moderated Homebrew Channel
Everything is run through a moderator to prevent piracy, but we still get awesome media players and stuff(If you wanna charge us for stupid [parasitic bomb], like half-assed MP3/AVI players, we'll just crack your system anyway and you won't even get money for the stuff that is worth money).
That is all for now. Maybe, if this gets more replies, I'll make a list or something.