Personally, although I like to level in PB I don't think it should be something you can sustainably do. A quest item reward would be nice.
Maybe something along the lines of midway between a 26 weap and a 30 weap for level 40+s would be nice, with a different skin ofc but not epic looking. Or an accessory item thats on the level of dring/kbrace.
Other than that though, the PB incentive is already there, super fast leveling compared to anywhere else for war/sin/tao, if they can't get a TS group.