Assumptions for creating this machine:
Rail with 2 probes on which they can move freely (possibly being able to measure 0402 distance), then having rotation and X/Y translation of that rail
Double (stacked) CoreXY arrangement where each head would attempt to stay within their square. See https://reprap.org/wiki/CoreXY . So if we assume single sided board and that we are figuring out connections of particular pad - One part of the board would be tested with one board and other with 2nd one - ie. at some point probe which stands still on a pad would need to switch.
Some videos showcasing various commercial machines:
join #libreboot @freenode for discussion