OK I'm more convinced than ever that Islam is not going to fight Topuria, and Topuria will be fighting for an interim title.
If Belal wins @ UFC 315 and doesn't move up to middleweight, I don't think Islam will vacate the 155 belt to fight Belal. And the fact that we haven't had a fight announcement means that Islam has yet to sign a bout agreement to fight Topuria.
If you're Islam and after UFC 315 you don't end up moving to welterweight, are you really going to be motivated to fight Topuria at UFC 317? I think Islam will find himself unmotivated. And then he and his team will decide it's not a good idea to fight at UFC 317.
In that scenario, Topuria will probably be given an interim lightweight title shot against Charles Oliveira.