Not just forehand or backhand but top spin or back spin, drops, volleys, etc.
The Top Spin 3 game lets you use 3 different buttons for 3 different kinds of swings/strokes. Maybe it will require more skill/dexterity/motor skills than most gamers have but it would be interesting if they gave you the option of executing all these different kinds of shots with subtle differences in motion.
Or in a baseball game, there are separate buttons for power vs. contact swings. If that can be done through motion, the former would be executed by generating greater bat speed or acceleration.
You might also have an uppercut motion, to try to get under the pitch and try to lift it.
More important is that you would have to swing low for low pitches, extend for outside pitches, etc.
In other words, you would replace a combination of buttons and left/right stick inputs with a motion which incorporates all these parameters.
But again, maybe the demographics of the Wii doesn't lend itself to games requiring or offering this kind of precision.
I think with something like tennis they could have the tilt, speed and forehand/backhand position 1:1, but the height of the swing would probably be fixed so that it would be practical for making contact with the ball. Maybe a high and low, but not 1:1. The same goes for golf and baseball.