Any chance the crushing wheels could emit redstone signal from their central blocks whenever they're processing something? I'd like to have a means to make belts bring items to the wheels and, as items start getting processed, the redstone signal flows to a clutch which then stops the belt from adding further items.

Hi, thanks for the suggestion.
Crushing wheels are pending to be reworked a little, making them able to be used horizontally and allowing ItemEntity-less I/O. This would solve the backing-up problem they currently have- but we can certainly add comparator output for the route you're taking as well. =)

Thanks for your suggestion, it has been added to our public submission sheet.