I have no doubt that it could support high definition. The only thing that I do doubt is that we will see HD-DVD or Blu-ray attachments for the Wii. The only way I can see that happening is if they come out with a second edition of the Wii with it built in and slighty better hardware. Because even though it could support most high deffinition resolutions, I doubt it could support 1080p video with the hardware that it has now. Even if it could I can't see Nintendo doing something like that since their systems are generally more about fun and games rather than home entertainment.
Yea alot of the things that I have always wanted game consoles to be able to do (like along time ago) they can actually do now. But now better technology has came out and I no longer have a need for consoles to be able to do certain things.
I don't foresee Blu-ray ever being integrated to the Wii, due to Sony's involvement with the technology.
As for HD-DVD, *maybe*, but that's a real stretch IMO. Nintendo isn't interested in cutting edge, they're interested in a different consumer market altogether, so it wouldn't make sense as a high-priority move. But I suppose that if HD-DVD won the race(Who knows at this point) and became truly standard(Yeah, that's at least a few years off, in reality), maybe, just maybe Nintendo would integrate it. But let's all recall DVD has been standard for years, and still isn't in the Wii; it's just not a priority. The fact that you can play videos from a memory card seems like random chance to me.
Quite frankly, I'm not in need of yet another media device. But in the future, who knows.