I'm just gonna throw a bunch of stuff out there.
One thing I would like(if Nintendo sticks with system codes) is a User Accounts option like Windows log in. That way if I'm using the console only my contacts show up, but if say my girl is using the Wii then only her contacts show up. that way no one is reading anyone else's messages or contacting someone else's friends. This also eliminates the need for friend codes on a game by game basis.
I also hope for a Free, but fully featured XBox Live rip off done in Nintendo stylings. I've never used XBL, but I hear it's about as good as your gonna find, so I definitely want Nintendo to copy the best things about Live and throw in a few things they might not have thought of. Better matchmaking, just knowing what your friends are playing while they're playing it and inviting friends to play when you see them on would be a big help in community building.
I have no issue with Awards (achievements/trophies) since they are an OPTIONAL task that any gamer can chase for a score that shows how dedicated they are to playing any and everything to completion. If you don't like Awards, don't chase them. But I could also see Nintendo tying Awards to post play My Nintendo Points.
"You've only received 4/10 Awards, you only get 20/50 My Nintendo Points for this game."
Ofcourse that only works with games you have registered, so that brings me to my next point.
Registration of 3rd party games and awarding of My Nintendo Points to go with them.
Nintendo profits off of every 3rd party game sold, so there is no reason to not be able to register them. They may not give as many points as a Nintendo produced game (3rd party game = 30pts / Nintendo game = 50pts), but it would still be incentive to support the 3rd parties and 3rd parties apparently need all the help they can get.
Also better prizes in My Nintendo. I know this has nothing to do with the Next Wii itself, but I'm hoping that the 2 will happen around the same time. New Wii, better prizes.
Motion Camera with Sensor bar attached. A motion camera on par if not better then EyeToy for increased motion tracking capabilities. No more disorientation of the M+ either.
Wiimote+. Wiimote with motion plus built in. Also a rechargeable battery pack wouldn't be a bad idea. if it got anywhere near 14-20hrs fully charged playtime, then it would be well worth it.
If the Vitality sensor is a hit, then I hope they find a way to integrate it into the controller. maybe turning the B trigger in to the sensor since that is the only button on the wiimote that would be comfortable to put a pointer finger in no matter how you hold the remote. The "Vitality Trigger" would have to be some sort of swivel finger encasing button though.
1080p graphics is already a given, and 3D capabilities out of the box with out a hit on performance just incase the concept ever takes off. Supposedly the GC and Wii already support it.
It should be able to play multimedia without hassle. DVD, MP3, whatever. media streaming out of the box would be great too. Or just encourage homebrewers to release their wares onto the WiiShop under an "Apps" section.
Nintendo too cheap to pay for DVD licensing? okay, put it in a DVD app that covers the DVD licensing cost. But lets just make it hassle free.
Built in storage. I don't care if it's a HDD (standardized and swappable), solid state or some of that holographic stuff they been working on, but make it happen. No less than 100GB to allow for all those new VC (GC - NES)/ WiiWare (upto 1GB) downloads.
Increased WiiWare game sizes. 40MB is too small & Developers are feeling restricted. Bump up the limit to at least 256MB but no more than 1GB.
Demos. 500MB - 1GB demo downloads. that shouldn't take no more than 30minutes to an hour on a decent connection and should be able to download in the background.
Background downloading and multitasking in general.
I should be able to download a WiiWare game from the WiiShop after reading a review on NWR through the Internet channel, but not exit the internet channel to check a message I just got that is making my disc drive glow.
Increased marketing support for everyone.
Something that incentivizes (is that a word) a 3rd party to actually advertise their own game. Like re-airing all Wii2/DS2 game ads on the Nintendo channel supporting original Nintendo Channel programming with Hulu like ad breaks.