Board Thread:General Discussion/@comment-4548390-20160910091011/@comment-16461120-20160910093446

Disney can't unilaterally alter film rights, contracts don't work that way, they'd need FOX's lawyers to agree that they would relinquish any challenge to the legal status of a property they otherwise have lawfully licensed.

In terms of the Skrulls, like the Maximoff twins, they're explicitly written into the contract as a shared property, and Kevin Feige said they are unique in that aspect, meaning there likely aren't any other joint custody properties we haven't heard of. He also said during that same European press tour for the first Avengers film that the reason they used the Chitauri was simply because they considered them a fairly clean slate, which allowed the writers more freedom than other alien races might have provided.