It is certainly what was implied:
I can't fathom the logic of upgrading me 5 days out for a flight to Canada or Mexico, but not being able to upgrade me at the gate for a transoceanic flight.
Since one can be upgraded right up until departure time now on a miles upgrade I cannot think of anything else they might be asking for.
And I cannot fathom it happening at CO or any other carrier. The potential lost revenue is too great, IMO.