Aren't you ultimately gonna have to figure out why you cannot change the speed on the GPU, regardless of the approach? And then you're just back at square one?

I think no one is doing it that way, because there is simply no need for it. Sure, when I'm 3D printing some material it sometimes need the heatbed to be exactly 45C or whatever, but why would I care about the specific temperature of my GPU? As long as it's not throttled when GPU utilization is at 100%, I'm good to go.

KISS :)