Yeah, I think that a setup like that would be more helpful for trimming off a little speed than for quick stops. Maybe just a little extra help if you're not feeling very confident in your brakeless riding.

My problem with the long descent thing is heat. Brakes are designed to be used for a couple of seconds and then allowed to cool. If you run them continuously (even if they're not gripping very hard) they will seriously heat up your rims causing one or more of the following lovely options:
1) Accelerated rim wear, which if left unaddressed will cause a pretty spectacular rim failure...hopefully not in the middle of that long descent.
2) hot rims -> hot tires -> expanding rubber -> BOOM! there went the sidewall
3) hot rims -> hot brake pads -> smelly gummy nasty rubber all over your braking surface -> very poor braking performance/brakes stuck to rim.