The individual boxes would be metal. I’m sort of envisioning each side having a couple of small, embedded magnets, to hold the enclosures together and also for positioning, to keep them aligned. The instrument connection, from box to box (apart from the end/terminal boxes, which would have a jack socket, too), which would be a couple of metal pads.
It would eliminate the need for patch leads and take up less pedalboard space. Of course, you’d be stuck with only that type of enclosure.