What you have described is an electronic drag brake. You would 'waste' any energy recovered by the system since you don't intend to use the "electrical assist" function of the hub motor. Why bother then? Conventional brake technologiies are way better at 'wasting' excess delta vee as heat than any hub motor/electronic controller combination existing. Our 2005 Raleigh Coupe has dual Avid BB7's with 160mm rotors. We've been riding it till the present time without any other kind of supplemental drag braking. 180mm or 203mm rotors have even more capacity to absorb heat and I simply cannot imagine a scenario where dual 203mm rotors would not be sufficient. Not even loaded touring.

H