I tried to use RUCs for the first time on an ATL-LAX-HNL-LAX-ATL routing. Only HNL-LAX was available at booking, so I wait listed every thing else.
Nothing cleared from the wait list.
ATL-LAX cleared at the gate. LAX-HNL did not, so I had the distinct pleasure of riding in C+ for 5.5 hours and got a grand total of two drinks. NEVER AGAIN.
Rather than play the game on the return, I called up, paid the difference, and switched to the HNL-ATL nonstop in F.
Bottom line is that inventory for RUC usage seems to almost never exist on long haul flights. I think it because the RUC is competing with those using miles to upgrade, as they both pull from the same inventory bucket. I got the impression that wait lists are meaningless for domestic RUC/mileage usage as well.
Obviously, this is anecdotal. But, personally, I will never play the battlefield upgrade game using an RUC again. I either won't go, or I will buy F.