A FlyerTalk Posting Legend
Join Date: Sep 2012
Location: SFO
Programs: AC SE MM, BA Gold, SQ Silver, Bonvoy Tit LTG, Hyatt Glob, HH Diamond
Posts: 44,324
1. If you had high AC status, I'd say 100%. As UA*G, it's hard to say. I don't readily have access to pax info to see how many people would be above you on any opup list.
2. It increases your chances of an opup to J, but there are currently 14 seats in PY (you said 10/40, it's 10/24) that would need to be filled before anyone would get an opup to J. Weight and balance is not going to be part of the process on this 77W. Any opups will be due to an oversell.
That being said, Y is overbooked. The 14 people you see on the "standby" list aren't on standby. They're confirmed pax without seat assignments.
Keep watching the app, as a lot can change in the next 15 hours, but generally speaking, you're going to sit where you paid to sit.