That sounds horrible. This is a central part of Gimp interface. Would it not make sense to fork into a different toolkit focused on complex applications?
GIMP's maintainer has half-seriously said that he's not even thinking about another GUI library change/port until after GIMP 3.6. I think we want to get more features available for users first, so we don't fall into same trap of 2.10 -> 3.0 where we mixed doing both at once.