OK, I have been playing around with an electric hose reel.
I have met nearly all Nathaniel's criteria. Powered on the water fed pole or van battery. Self layering mechanism- your hand as you let the hose run through a cloth to clean. Better than remote controlled, just move a handle towards the reel with your right hand as you layer with your left. No holding drills at awkward angles, and no kickback from the drill at it starts to turn.
I have it mounted on it's own frame which attaches to the bolt down hose reels I fit to vans. It has a lever mechanism attached to the speed control. Works very well and I will probably fit them as standard in any new systems I do.
Before anyone asks the mechanism won't do for any drill, and it wouldn't fit on any hose reel.
I would welcome any feedback
Peter