The board I designed using #LibrePCB is finally on my workbench, it was produced and assembled by PCBWay. This is an expansion card for any SBC with a RPi-compatible GPIO header. It can multiplexe USB 2.0, HDMI 2.0, Gigabit Ethernet signals, and it has a couple of relais to switch power/pin state. We are using this kind of hardware to validate SBCs using other SBCs