gimp isn't being held back by money, they have over a million in bitcoin just sitting there from an old donation that grew in value. In over a decade, no one has figured out how to pay the taxes on it if they start using it to fund developers.
I read on reddit a long time ago that a UI designer tried to help improve gimp, but the devs were hostile to it (i may be remembering that wrong though). Considering how long its been with no UI improvements, I don't think gimp will ever revamp its UI. Instead, I think Krita has a good chance of moving into photo editing with enough funding.