In reply to Jon Read:
> This sounds like a terrible idea from the perspective of not trashing the rock.
It doesn't necessarily have to be. The amount of force a climber can exert with a manual brush will be pretty high. Maybe a more complex motorized brush with individual brush elements rotating or oscillating could be designed to get more chalk off with less pressure than a brute force scrubbing brush. Like an electronic toothbrush isn't supposed to be pushed really hard against your teeth, some of them even have indicators that you are pressing too hard.
Also, the main use might be inside where trashing the rock isn't a consideration and gyms might be willing to fork out more for a shared brush. It could possibly incorporate some suction to immediately get any chalk dust contained. If it worked well and kept the holds cleaner it might mean circuits needed to be stripped less often.