Gates Carbon Drive off-road experience?
The main problem I see with Gates Carbon Drive on a fat bike is that you have to have a frame that "breaks" in the rear triangle to accommodate threading the belt. Have you checked to make sure there's a frame available that supports fat bike tires and also supports breaking the chainstays. As far as off-roading goes, that would create a potential weak spot in the frame. Although I"m sure any quality bike manufacturer would account for that when building such a frame.