It would be really handy to have a 3rd controller in addition to the master and slave controller. That being an output controller, that way anything that can't be sorted into a drawer gets spit out the output controller.

The use case I have in mind is a long mine cart track, where I send carts full of items from one end to the other, and a hopper removes them on the far end, and sends them into the storage controller. In my case if I send stuff I'm not keeping in drawers it clogs up the hopper and the whole system stops. If there was an output controller those unsortable items could be ejected up in my base into a regular chest that would accumulate the random extra stuff.