So it sounds like the "[X] class requested" has replaced the old "Waitlisted" nomenclature. I think conceptually an upgrade list is just another waitlist, and there's probably some separate process that pulls the correct supporting instrument. When those processes don't run simultaneously, or when the second process fails to run, you wind up on the waitlist but without having supported the upgrade.

It makes sense that there would then be some followon process to audit the upgrade waitlist to be sure that instruments have been pulled before you're cleared from it.

However, some have reported that, in this scenario, the GA will ask you to support the upgrade at the gate, as s/he is running the upgrade list - and that if you can't support it, you'll find yourself in a bad Y seat. This implies you had already lost your carefully selected Y aisle or bulkhead or exit row seat, which implies that the upgrade had already cleared.

So if this happens at the gate, the GA is prompted to ask you for an instrument and downgrade you if you don't have one... what happens if you get to the top of the upgrade list and R inventory appears, before it goes to the gate? Will the system skip you and/or remove you from the waitlist?