But there is an ironclad contract. That's law, and something that has been slaved over quite a bit.
So let's cut thru the BS: you guys trust Marni and don't think he would lie, and are sticking up for his word. And I don't think he's lying! He's just most likely getting half-correct information, he even said this was a possibility on Magic. But contract law does not lie: unless there is a deal with TWDC and Comcast about GotG theme park rights, which due to them being publicaly traded companies we would hear about, there is no way this specific attraction can exist. Could this happen? Yeah, I think it might but the deal would be quite significant for something as possibly flimsy as the Guardians IP, which has been only popular in its exact state for 2 years.
Now you can argue against that, but the contract itself has been long dissected and would take a lot of legal pummeling and twisting to get anything out of it. It's easier just to make a deal, it's that solid. If they could twist things around then things would've sprung up at WDW long ago. Instead there's proof of the opposite: Big Hero 6 was fully separated from Marvel Studios and in look and concept. You can immediately make the argument that this is "Disney's Big Hero 6" and not "Marvel's Big Hero 6", which is a "separate" property. But GotG is "Marvel's Guardians of the Galaxy", no getting around that. And they're joining "Marvel's The Avengers" in 2 years. So with BH6, Disney made a concious effort to separate it and that's why the Baymax M&G exists. Hell, what if BH6 was the coaster? (totally unfounded speculation here)
That would be a legal, easy way to take advantage of a "Marvel" property that ties into the theme of Future World. Hell, Chapek can even have a nice big gift shop full of sellable Baymax plush. That's way easier than GotG. Not sure why Disney would even bother.