The Wii seems to have an interesting mix of a user base. In the end, I think it's very similar to the DS.
-They have the new gamers, the ocean of everyday people who wouldn't have picked up a game system before the Wii. The DS has these as well with the "touch generation."
-They have the Nintendo fans, people who always buy Nintendo's systems so that they can play their favorite games.
-They have a good portion of last generation casuals. These people buy game systems on pretty much nothing but hype and quantity of games.
-They have the lapsed gamers, people who haven't bought a game system since the SNES or earlier.
-Then they have a mix of core gamers and PS2 owners from last generation who couldn't or didn't want to cough up $400 plus for a game system (count me in this one). You'll see that there are actually quite a few of these if you check the topic about how many Wii owners had Gamecubes.
As far as the ages of Wii owners go: They have most of the children (ages 13 and under), almost none of the teenagers, a split market in college, and the majority of the adult market.
Looking at the odd patterns of Wii owners it seems that the Wii will need to carry a very diverse library of games to keep everyone happy. Sure some games may appeal to everyone in that list (Super Mario Galaxy), but others will be niche. A game like Red Steel or Resident Evil 4 can sell well on the Wii, but at the same time Mario Party 8 can be a booming success.
As far as future games go, something like Metroid Prime or No More Heroes is going to appeal only to the core audience gamers on the Wii, but will likely sell well anyway, whereas something like EA Playground is only going to appeal to the children who own a Wii.
The Wii (and really the DS as well) is such an interesting phenomenon because it has easily the most diverse and ranged userbase ever to grace a game console. The potential variety of successful games on the Wii is boggling, and it really is becoming a system that has something for everyone due to it's success and diversity. If you look at the current range and variety in the DS library, as well as the range of what sells well, I think you will get a glimpse into the future of the Wii. It's also notable that the DS continues to gain core games and very strong first and 3rd party support.
