J1 could be debug, but what's the sense of having one on every production machine? Usually you only need debug on your development lab box, and at most a production machine would have an unsoldered place for a connector. It's 26 pins which does correspond to the BDM debug connector for the Coldfire processor though. I realize it's not an enormous expense, sometimes you'd leave that sort of connector on for the very early run. Likely it's used for manufacture test and perhaps startup/burn in, not debug. That would make more sense, and that would be my guess.
I'd so much more like to dream it's some magic mysterious expansion connector though. Actually a factory test connector often does have some interesting signals, and if this is the BDM then it's got a spec
A Coldfire processor, hmmm, the Digitakt would be awful fun to hack, and at $650 worst case loss i could see doing that. I assume it would be pretty easy to open up the download OS too now that we know it's a Coldfire processor, and hack it without opening the box.