Nintendo have pushed a new Wiimote controller for their Wii console through the FCC, though it's unclear what functional changes the new model will bring. Listed as model RVL-036, the diagram makes it clear that this is indeed a Wiimote but the confidentiality request locks up any live photos or the user manual until November 7th 2010.
The most obvious possibility, of course, is that Nintendo have integrated their MotionPlus technology into the new controller. Currently available as a snap-on accessory, MotionPlus increases Wiimote accuracy in certain games that support the system.
Alternatively it could simply be a different design of internal hardware, with manufacturer Hon Hai Industries (aka Foxconn) streamlining the build process so as to save money on each controller produced. We'll have to wait until later in the year to find out for sure.