Not really. UA sets it upgrade liability by limiting upgrade space. And given there is a waitlist in most case, that space is nearly all utilized. So, take x GSs out of the mix, there is no decrease in upgrade utilization -- someone else makes use of the space.

For your proposal to work, which seems to lack GS support here, UA would have to decrease upgrade space and find others to fill those seats. This is what is mean when folks state there is none / low incremental cost to UA for upgrades (plus it opens up space for more economy sales. The economics don't yield the proposal's benefits for UA and comes with extra costs/crowding and diminishing the uniqueness of PLs.