I always envisioned a slotted plate , open at the rear, attached/ brazed to the bottom of the the chain stay. Sort of a reverse facing horizontal drop out. The reaction arm would have a bolt or stud going through the end ( at the spot here they normally have the attachment hole) that would sit in this slotted plate. The reaction arm only needs to prevent the hub innards from turning; it doesn't need to be bolted down. The normal axle bolts could be loosened and the hub slid first in one direction to release the reaction arm pin/ stud/ bolt, and then in the other direction to free the wheel from the frame. So simple,- no quick release or bolt needed on the reaction arm. The slot, in this plate, would only need to to be long enough to accommodate the range of available reaction arms.