Hmm I'm a bit late to this discussion.
I think it's better to use a lower torque motor that's geared down, for reducing unsprung mass.
Turnigy AquaStar T20 3T 730KV/1280KV Water Cooled Brushless Motor
Watercooled, 2.1 lbs, 5kW peak power. Attach to the spindle, put a pinion and annular ring gear sort of thing on the rim. Should be no more than 3lbs increase in unsprung mass per wheel, the equivalent of going up a rim size or two. Looks to be completely sealed.
Regeneration with that is more complicated than with brushed permanent magnet motor but I imagine it can be sorted out.