Is Wii Fit what you bought a gaming console for? Also will the millions of people who buy Wii Fit also be the type of people that'll buy hardcore Nintendo titles such as Super Mario Galaxy, Super Smash Brothers Brawl, etc? If not what will bringing them to the console accomplish besides selling more consoles (for bragging rights) and having third parties scratching their heads and wondering what to make that'll appeal to the majority of the userbase.
Also in my experience many people who buy home exercise equipment seem to lose interest in it after a certain length of time and simply start using the equipment rarely or not at all. While I'm sure Nintendo will be able to come out with one or two fitness programs or games that'll appeal to people who solely buy it for the fitness aspect will it be enough to keep people interested in the long term (for years)? If not it might simply lead to many Wiis bought for Wii Fit eventually collecting dust in livingrooms and closets.
