I hear what you're saying, and I've tried to get it solved at the gate in order to give the opportunity to the next person in line, but I'm not about to take an unwanted upgrade because UA's systems can't handle all-or-nothing upgrades at the gate. The simplest solution, when it can't be solved at the gate, is to give the upgraded seat to the person in the seat I want. The person on the top of the upgrade list might not like it, but their situation is no worse off than if I'd stayed in my assigned seat.