Also, creatively speaking, there is absolutely no reason why Marvel can't start cross-pollinating characters or story arcs IF THEY WANT TO. Marvel can take an advisory role on the Fox movies and own complete creative control over their own movies. Fox can basically show Marvel their final cuts and ask if they would like to seed something in there. Also, there is nothing now that is going to stop, say, a FF reference or even characters showing up in Avengers 4. Coz, even in the worst case of the deal being stopped (and at this point there is no reason for it to be stopped), those rights will most likely go back to Marvel.
Some folks just wanna spout baseless negative stuff.