Nintendo was pretty bullish on the motion controls and drastically reduced the number of buttons on their controller, probably because they wanted to force developers to use motion gestures. This has (overall) worked out both well for Nintendo (almost all games use waggle) and poorly (the current Waggle controlls are quite limited). The Wii MotionPlus has demostrated that there is a lot of room for improvement in motion controlls, but even Miyamoto admits that motion gestures are not ideal for all games.
With that said, I would expect all controllers in the next generation to be similar to the Wiimote and Nunchuck with enhanced motion caputure and to have more buttons with enhanced functionality. By simply putting the button layout from the Gamecube onto the Wiimote (while dropping the d-pad) and including analogue triggers the Wiimote would be able to match all of the functionality applied to the right hand of a conventional controller with the added motion controlls; at the same time, the Nunchuck can remain very similar to its current form with enhanced motion controls and match the functionality of the left hand of a conventional controller with added motion controlls.
In other words, why would anyone stick with conventional controlls when it would be so easy to merge the two concepts together.