No one has dove into anything on the motherboard that I am aware of. If you feel frisky enough, please provide any technical details you come across.
Just for conversation, I would look at the parameter wire sensor. See if you can figure out how to tap into that, or what the output data looks like (I'm guessing it'd be 1/0) and then watch for it to go into whichever state is on the parameter wire, tell your board to wait 5 seconds and if it is still on the parameter wire, it's probably going home. You may still get false alarms in the corners where the bot may be bouncing around the wire for a bit, but you could probably compensate for it.