Depending on the aircraft and equipment but...
It is safe to say all the 8-seat A319, 12-seat A320, 12-seat 737 are in the 'forget about CPU/RPU' categories in hub-to-hub. If you are fortunate enough to be in one of those high density 777-200s, then at least you have a shot.
Think about the A319 in IAD-SFO, DEN-SFO, SFO-SEA on Mondays, Thursdays, Fridays, or Sundays? I'd just not even look at the upgrade standby list. That may actually make me feel better to just secure the bulkheads or exits on A319/A320 PMUA, as those are really comfortable seats.