Originally Posted by
zoned_post_meridiem
... Second question (I don't usually do these upgrades, so fairly ignorant about how they work) -- is there a way to gauge whether this would clear (I'm not sure what fare class rules apply here), and if they clear, do they usually clear at the gate or much earlier? ....
Impossible to answer in the abstract other than generally chances are poor unless you have high status (and then still might not be great). But it can happen.
Status, purchased fare class and time of request is the basic system but lots depend on flight specific factors -- route, day of the week, season, historical booking data, .... the discussion in
[Consolidated] Chance of upgrade clearing on my flight may provide some insight.