Its great in theory , but what you would have is a serious game of dodge ball, nobody would fight anyone dangerous. , now if there was an incentive on top of the agreed purse, that would help. Or a non performance penalty, Example like for heavyweights. A fighter comes in 15 - 20 lbs over his best fighting weight , penalize his purse. I think things like this could help fighter stay focused during training .
but really in the lighter divisions fighters are usually are at their best. its the Heavyweights that blow up into worthlessness. Just my opinion