It is possible for the fight to happen if Inoue is willing to take the risk. However, as long as he is under the Top Rank promotion, it might be challenging for him to make his own decision and prove himself against a tough challenger like Casimero.
Personally, for me, it doesn't make sense.
Why Naoya Inoue or Top Rank promotions should adjust for that possibility just for the reason that Inoue should prove himself against a tough challenger? Regardless if a challenger is considered tough, then make their way up to be eligible for the title match.
In the first place, Casimero's camp is the one to blame for why the chance of fighting against Inoue didn't happen. Therefore, he should be the one to make adjustments, not Inoue or Top Rank making that move. I'm with Quadro Alas, of course, against Inoue, if they will fight. However, if only Casimero's camp did the right thing, he should be the one fighting Inoue in the Undisputed Title Match at the 118 division and not Paul Butler.