Casimero is only in the rank 7. If anyone deserves the shot to a title, it's Luis Nery but even him was skipped by Innoue all for unification. There is a possibility that Inoue will move to 126 lbs and probably skip all but challenge Robeisy Ramirez. After all, he already beat Fulton which is below Robeisy so fighting Fulton I think is more of a strategy to get the WBO belt from Robeisy.
The most exciting is the welterweight class which I think Inoue will stay longer to fight top ranks.
Depends on which division you are going to look for Casimero. But obviously you are talking about the WBC so yes, he is number 7 and Nery is number 1. However, as we have been discussing, Nery is banned to fight in Japan because he was once caught using a ban substance.
If Inoue wanted to fight him, then it will be outside of Japan. However, Inoue doesn't want to go out in the US, he defeated Donaire and recently, Stephen Fulton is his hometown. And most likely, if this fight is going to happen, it will still be in Japan as well.