While I could be wrong, I think their next system will go "in both directions" at the same time ...
I remember reading an interview a couple of years ago where Miyamoto (effectively) said that he still saw value in buttons and analogue sticks but the Wiimote was designed with as few as possible (in each orientation) to force people to use motion controlls. While I wouldn't expect Nintendo to go to the other extreme, I could see them incorporating more buttions, sliders, analogue sticks, touch pads, or (pretty much) any conventional input device onto their controller if they thought it added value.
At the same time, Nintendo seems to be trying to maintain an asymetric market so that they're not in direct competition with anyone; and (as a result) I would expect them to do something different with their next system that no one else is in a position to try.
