I am not looking forward to the LAN feature of Mario Kart. It is a cool option to have in a game, but that probably means no online feature.
Online, to me, is much better than LAN. LAN is fun and all, but online lets you play against a braod userbase at any time. Eight friends are hard to gather, especially during the school year.
This could have been the game that could launch Nintendo's online feature. But, alas, the cost of setting up online is too much. This game alone cannot pay off the cost of online. Still, if Nintendo and a couple other third-parties has more promising multiplayer games lined up after Mario Kart, I do not see the harm in setting up online. The games could pay off the cost of online and finally gve GCN owners who do not have a Xbox or PS2 the chance to go online.
I doubt we'd be seeing that anytime soon though...