I'd like to see more game take advantage of online playing. Some classic board/card game for online play with Mii's such as poker, chess, checkers... and maybe more modern board games such as Risk, Monopoly etc.
Wii bowling is pretty captivating but it needs more variables, ball weights, ball materiels, floor conditions. Online play, maybe leagues and tournaments. So much is possible for the Wii in these areas. They could even add in fun stuff like cosmic bowling, and if there was a way for voice chat it would really pull the game together, cause part of bowling is taunting your friends when they choke.
And for something completely different lets make a "Ninja Warrior" game, like the Japanese game show obsticle coarse where they basically run the gauntlet and have limited time to get thru the course.