Combined with my pyboot tool[2], automatic bisect is as simple as:
git bisect run '(rebuild; pyboot <board>)' and it's fully automated
There's also a network standard for this stuff from IIRC National Instruments which I believe is most likely what the network controlled switches Paul Walmsley is using implement. I'm intending to give that a spin when I get round to sorting out auomated power for my boards.