I'm sorry but I believe this a mistake in priorities. This is an image editing program. The UI is the core functionality. They could cut half their features and focus on a better UI and it would make it a better program.

There are web-based photoshop clones that offer better usability than GIMP. I shiver in disgust saying this out loud but it's true at this point. They're slow, more minimalist in terms of features but they don't have buttons that overlap or scroll bars popping up out of nowhere. The GIMP UI is an unusable mess. It's the UI equivalent of "programmer art".