There is a high chance that there will be a trilogy if Donaire will win on their rematch next month as their standings would be tied to 1-1 but if Inoue will still be the last man standing then I think he will go for Butler and go up to another division after he defeats Donaire and Butler respectively. In the past, Casimero is included to his plan but now that Casimero has been stripped of his WBO belt, I don't certainly think that Inoue will be interested to him anymore.
Honestly, there's no other fight that should be arranged but a trilogy if ever Nonito Donaire wins this rematch against Naoya Inoue. It's like the chapter of them should now be close for good. For sure, once the winner of this rematch is announced, and let's say it's Donaire the winner, Inoue will immediately ask for a rematch on the post-interview and Donaire will gladly accept it right away.
The boxing association won't miss the opportunity to make another round of money so if ever Nonito wins this fight, we can possibly see another rematch between the two. Trilogy often happens when the fight record between two boxers is 1-1.