Actually it's not necessary anymore, Donaire and Inoue have proven that they can reign in the bantam weight division, so their fight is just a matter of knowing who is the best that will hold the unified belt. Donaire vs Inoue is undoubtedly the biggest fight next year in bantam weight division, even Casimero could not ruin that.
We know Both of them is already a recognize good fighter already but Donaire has been defeated by Inou on their last match so its necessary for Donaire to have a rematch to Inoue so that he can revenge back and regain his reputation that he is the best on his weight class. But I think this will not happen since for sure we will see more elite fights from Inoue and maybe Donaire next year will totally hang his gloves and retire, but I really want them fight so hopefully we can see this to happen.
What I'm saying is it's not necessary for them to have more fights before the rematch. I have a good feeling that the rematch will happen next year as promoters will definitely have no problem setting this fight, the only difference now is probably the split of the revenue as both fighters are popular and champion at the same time.