There is no end of contract date concerning Island of Adventure Marvel Rights. It is mentioned about Avengers being a no-go. Fantastic four and X-men are no goes also for WDW.I think this could be a 5th park for Disney World. I'm speculating it's going to be an IP-themed park based solely on Star Wars. The Galaxy's Edge over at HS, while pretty neat, proved to be underwhelming for some visitors and the fact that it didn't seem to be all that popular at Disneyland proved this. Some fans wanted an actual theme park based on many different worlds of the Star Wars universe and were very disappointed when they saw what was built. Then Disneyland is getting a new section called Avengers Campus or something, and it will have some new rides based off of that. More than likely something similar would happen at DW eventually, and I believe this might be that. This new park would probably be half Avengers and half Star Wars, both to appease fans and to compete with Universal.
The motive is not there for either side for WDW getting Marvel Rights. Universal makes money off marvel, but Disney makes money off the Marvel Section of Islands of Adventure also. To top it off, I don't see Universal giving up Marvel anytime soon. Universal has space to pull more stuff besides the Epic Universe theme park. Universal has a lot of money tied up in that 3rd park including road construction costs.
The only known Marvel rights WDW has is Guardians of the Galaxy, Big Hero and the Eternals. I think WDW can use Doctor Strange because they had a Doctor Strange meet and Greet at DHS when the first Doctor Strange movie came out. I have no idea on Shang-Chai and the legend of 10 rings. Basically WDW can pull off a Super Hero land from the material they have, but not enough for half a new theme park.