i really don't see the point even for multiple brakes on one wheel, if you were controlling a disc or drum and then something on the rim it wouldn't make sense to pull them with the same pressure,

if you were pulling two with each, so one rider could control both the drum/disc set ups with one lever and the rim set ups with the other i still don't see how this would make sense,

when i think about someone with one arm ridding a mountain bike or hybrid it makes all sorts of sense, when kayce said polo i can see it there as well, also maybe on a jogging baby stroller where the brakes aren't really stopping very much momentum?