Earlier quoted context omitted.
Well, given that it is open source software, have you ever considered contributing? I'm not trying to be dick. I know that just because you can spot flaws doesn't necessarily mean you know how to improve them, nor are you obligated to just because it is open source. But I bet you could offer some valuable feedback and/or ideas.
There is a tremendous amount of inertia that most be overcome to make changes to the UI. I don't just mean technical inertia which is probably large given GIMP's size and long history, but also people inertia. UI tends to be the ultimate bikeshedding [1] blackhole. Few people have an opinion about how a denoising filter should be implemented. Several orders of magnitude more have feelings about the UI should look and…
You could conceivably raise enough money from stakeholders to do this properly with a few experienced UI developers, proper user testing etc.