Reporting a successful data point for self service -- booked an itinerary just for myself that was showing the availability indicator (and Z was also being sold) and was mildly surprised to see the checkbox to apply an RUC (I swear it had gone missing for me for a while).

I forget if the upgrade part of it went through instantly, as my attention got diverted after completing the booking (squirrel!) but I received the usual ticket receipt plus a separate email* about upgrades clearing, ~3 minutes apart, which reminded me to go back and change my F seat assignments (both cabins are essentially wide open but it auto-assigned me to 4A on one flight and the bulkhead row in the other )

*In fact, they sent me 4 copies of the "congrats your upgrade has cleared' email