I can imagine a whole line of Wii Sports sequels:
Wii Xtreme Sports, featuring base jumping, rock climbing, sky surfing, etc.
Wii Water Sports, featuring water polo, 100m backstroke, etc.
Wii Team Sports, featuring soccer, basketball, etc.
I'd still really like to see a wacky arena paintball game. It's Nintendo's ticket to do for FPS games what they did for fighting games with Smash Bros.