MotionPlus functionality, commenting "as to looking at whether or not it will be an attachment or built in - we're always looking at how hardware should evolve and where we should take it." He also added that "it's something we'll be looking at."
Of course, there are several things to consider. For one, how much would it drive up the cost of the Wiimote? Secondly, how crappy would it be to have to (eventually) buy all new Wiimotes? Thirdly, until Nintendo shows off a killer app for the thing (as okay as Wii Sports Resort looks, it's definitely not a killer app), does anyone even care?