Something big is in the works for the Xbox 360 Spring update. How big? Well besides the gi-normous list of rumored updates we're now hearing from a number of sources that the Live dashboard is going to be getting a second interface option, one that will use the yet-to-be announced motion controller to navigate.
Here is the article:
http://heartbroking210.blogspot.com/2008/07/xbox-360-to-get-3d-dashboard-makover.html

I'm looking forward to the rumored major overhaul of the current dash, but I doubt it'll be 3D. Also highly doubt it would be limited to users who buy a specific peripheral.