Neat project. These popular "commodity" devboard designs have been remixed and copied so much that it was just missing an open-source design to slot into many existing projects. I can imagine designing a board using one of these designs as a "template" but adding whatever capabilities I need, then knowing it fits a standard footprint.
Yeah, I've designed PCBs around PCBs—most recently around the LILYGO T-Display because it had an integrated LCD. I ended up adding my own DACs to the "mother" board though. It would be nice to have a single PCB that combined the best of both.
(I still wonder if I could compete on final cost though.)
