I doubt it will be as big as Wii Sports in Japan. The market is overly saturated with those kinds of games already thanks to the success of the first Wii Sports. Remember these people are not core gamers, they are casual gamers and they might not end up buying the sequel even if it comes with an extra peripheral, because it could be meaningless for them. Had the market remained balanced (without so many sports and mini-game collections), Wii Sports Resort would have been bigger IMO.
Many of these new gamers could be satisfied with Wii Sports and all the other sports/minigame collections released in such a short period of time, so WSR will not be an essential buy for them. I'm thinking the same about Wii Fit+, but the thing is it's coming out faster than WSR did in comparison to Wii Sports, so there wasn't enought time to flood the market, even though it's becoming saturated quickly with many fitness games announced for the rest of the year.
Reggie is right about the Red Ocean status that fitness games are gaining. What I don't share is the practice of releasing a peripheral and then never supporting it again. WM+ shouldn't just be a peripheral, it should be an almost obligatory purchase for Wii owners, since it's enhancing the quality of the console. What WM+ will do is divide the audience if it's not bought by most of the people, and that's something no developer wants, because then you are having a console with a userbase that's now smaller than the competition's.
Proud poster of the 10000th reply at the Official Smash Bros Update Thread.
tag - "I wouldn't trust gamespot, even if it was a live comparison."
Bets with Conegamer:
Pandora's Tower will have an opening week of less than 37k in Japan. (Won!)
Pandora's Tower will sell less than 100k lifetime in Japan.
Stakes: 1 week of avatar control for each one.
Fullfilled Prophecies