SSX3 was the pinnacle of the series and was an amazing game. If you were burnt out by then, you missed out on a great game. I didn't play SSX or Tricky much, but 3 was an outstanding example of tweaking the formula just enough to make it completely awesome.
This one - so far - looks a lot like SSX3. If it retains the visuals we found there (or improves them, please) and all the openness from the game, as well as the absolute INSANE amount of replay, this will be one hell of a game.
Adding online would seal the deal as quite possibly one of the greatest snowboarding games ever.
As far as Mii speculation goes, I wonder....as games come out where Miis could be incorporated, do you think you'll get access to Customization packs? I.e., SSX gives you a "SnowPlay" pack, and you can add scarves and hats and gloves to your Mii. Nothing huge, just enough to make them fit the game in question.
It would be nice if you could have the packs usable in other games, but I doubt it. You'd have to load it to the hard drive inside, and I don't think Nintendo originally planned for it.
Would be a cool idea though.