I was going to do something similar with a USB keyboard hack in each panel, I have a cab thats currently a 2 player thru the use of stainless steel plates about 300x180mm with the jstick and 6 buttons on each, they are in a ply top.
I was going to make a new ply top, and make 4 drop in modules, each with a stick and 6 buttons, and then make a few more with the alternate sticks or wheels etc. Being USB with a keyboard hack for each, I wouldnt have blocking issues between the boards (I hope)