Does NW ever upgrade elites who have already boarded? I have seen this on some of the CO flights I have been on, but now that I think about it, I can't recall ever seeing it on a NW flight.

The current system seems rather a gamble; if one waits at the gate long enough for the waiting list to be processed, that usually means boarding last and no carry-on luggage. On my most recent flight, that would have been in no small part due to the FAs' luggage consuming the first two bins in coach, the coat closet, as well as the seat in FC some (off-duty?) FA appropriated for herself.