I'm not saying it's a lock.. it is just fun to speculate about, as much fun as any other scenario. I really don't have much else to say about Jon, in this thread.
You see, I don't think Euron is that clever. I don't believe Euron is waiting in Slavers Bay to pull a fast one on Victarion. I believe that Euron is much to sure of himself, and I believe that Euron is depending on the dominance that he thinks he has over Victarion. I don't think Euron has even considered the fact that Victarion might double cross him. In my opinion, Euron is relying on the psychological hold that he has had over Victarion his whole life.
I dont think it's possible for Euron to play Victarion like a fiddle, because there is no way for Euron to have known about Moqurro. Even if Euron was playing Victarion in the beginning, Moqurro is the one playing them both now. Euron might have already binded the Dragon Horn to himself, thinking Victarion would not know how to do that, but that's where Moqurro comes in, but I don't think Moqurro will allow either one of them to bind the Dragon Horn to themselves, because Moqurro is in favor for Dany. Moqurro believes that Dany is Azor Ahai, and Moqurro knew from the beggining that Victarion would BR the one to take him to Dany. So there is no way that Moqurro would have ever gotten on a ship to go to Dany, if he knew that he would have to give away Dany's dragons to get to her. So that means that Moqurro knew that he could keep Victarion from getting Dany's dragons, while still using Victarion as a ride to get to Dany.