I'm skeptical. Disney owns Marvel, so putting a Nicekodeon area in makes no sense. However, they still have a contract with Universal. Why then, would Universal build an entire theme park knowing that Disney can swoop in any moment?
There's been talk of some strawberry fields slightly northwest of Disneyland where a third park could be put, and a fifth park has been debated in Florida. My best guess, though, is that these are old.
These pieces of concept art are old. However, due to Disney, I have a feeling that the Nicktoons area won't be in the the park. This is just a guess, by the way. Anyway, that idea about a fifth park would be very cool. I would love to go to Marvel's theme park if it was in Florida. Heck, I actually THOUGHT that it was in Florida until I found out that Dubai was a country.
EDIT: Universal does have a section in one of their parks with a Marvel theme. It's in Islands of Adventure, and the second (or final if you go to Seuss' Landing) section of the park that you can visit. It's famous for its Spider-Man ride. Speaking of which, do I detect a Spider-Man Tower of Terror ride?