Nintendo of America president Reggie Fils-Aime has assured Wii owners that more MotionPlus games are on the way. There may not be a lot of games that support the add-on now, but there is "tremendous support" for it. The trick is in determining whether or not it's right for the game.

Speaking to MTV Multiplayer, Fils-Aime said:

There's tremendous support for Wii MotionPlus. First, what it would highlight is that Wii Sports Resort continues to sell exceptionally well. In addition to that you're seeing some fantastic third party support. Red Steel 2...about to come out. And from a first party perspective we showed Fling Smash. There are more titles that are coming, it continues to be a core part of what we do.
The next Zelda game is expected to feature support for MotionPlus and Shigeru Miyamoto is rumored to be working on another MotionPlus game. But what about Nintendo's other franchises like Mario and Metroid? Reggie explained that it's not about shoehorning the add-on onto whatever games they can, it's about what's right for which game:

But I guess what's unique with Nintendo is we don't force our developers to stick to a particular type of control scheme, and you've seen that. Everything from the new Metroid title to be single remote driven to Fling Smash utilizing the Wii MotionPlus. So it's all about what's right for the game.
Via MTV Multiplayer