Making UIbuilder more consumer friendly might allow the average player to move some stuff around to where he wants it but it will not make mods better. For the people building the more advanced mods it's probably not going to do much anyway because less time is spent on doing layouts than on working around UIscript bugs.
In my opinion the hypothetical budget for an UIbuilder makeover would be better used for a makeover of the UI core (LUA is something that got mentioned a while ago, and I cannot post on a topic like this without mentioning the persisting lack of Unicode compatibility in current UIscript
). This would result in better mods for everybody.