The game will also apparently have a more streamlined online interface as well, with enhanced matchmaking tools. Though some have speculated this might mean the elimination of friend codes, it seems unlikely Nintendo would abandon the frustrating but supposedly family-safe community system it has been championing since the system's launch.
As stated when the game was announced at E3, the title will also be bundled with a racing wheel peripheral. Seeing as the heavily anticipated Smash Bros. Brawl was delayed until February 10 of next year, it's probably safe to assume the spring 2008 general release window for Mario Kart Wii will lean toward the latter part of the spring months to avoid making consumers choose between two first party Nintendo titles.
This should be fun. I used to network my old Gamecube with another one at a friend's place and we'd have about 6 or so people playing at once. 12 people playing at once is going to be crazy.