This may be the official line, but I think there is a lot more discretion at the gate...perhaps less at N American airports than say [insert your favourite China airport here], but discretion just the same. An electronic system might make things more transparent, like other US carriers who display the J standby list on the screen by the gate, and also allow for some data continuity so that things like one's rank order on the pre-checkin UG waitlist can be considered.

On another note, I agree with the idea of auto-upgrades to empty J seats, within reason. Certainly tier baed (SEs and high-mileage Es only - maybe a threshold bonus) and only on Executive Class (not Executive First) routes. Compared to other North American carriers the AC J products are pretty good, and it would be a shame to have the quality of the experience suffer if AC has to budget for a consistently fuller J cabin.