I think for underdog bettors this is really a good odds assuming that Donaire can still fight and has the power and the timing to counter Inoue when he is going inside just like in the first fight. Donaire though will need to have a lot of stamina against the young Inoue to be able to sustain his attack the whole 12 rounds because this is what I'm seeing in this fight. Back and forth war throughout 12.
The only chances i can see for Donaire to get the win is to either control the early rounds or knock Inoue down even once and then calm down and just defend on the late rounds. I mean Donaire's style of play tends to be aggressive on the early round and then gas out on the later round, causing his punches became weak.
Inoue is known to have a destructive punches, if Donaire gas out on the later round he'll most probably gonna make that as an advantage.
But it's hard to see Donaire knocking out Inoue early, Inoue has also a good defense and a solid chin and I would say that he has a good boxing IQ as well. Donaire for sure can be aggressive in the early rounds, but he can't just cruise late in the rounds. He still has to give everything he got because Inoue has a good stamina because obviously he is the younger of the two. For me, the key for Donaire is to uses his counterpunch as his main weapon and make Inoue makes mistakes instead of looking for a early knock out.
He must find a hole for Inoue in order to take him down as he is firm and strong that he can really take a hard punch at their first meet. For this rematch, he must have to be more aggressive as this is the only way Inoue can make preparation for the next move.
They don't have a long age gap that is why I don't weigh this as a factor as experience is really an advantage when it comes to boxing sports.