Well, technically, Disney can build anything Marvel it wants in any of its Orlando parks provided that the character(s), or the "families" of those characters, used by Disney are not already used in a more than incidental manner by Universal.
Disney could try and establish a precedent to see just how much it can get away with in regard to meet & greets or hotels or restaurants outside the parks too, but why would they want to give essentially free advertising for the competitors park up the street? I can't think of a more effective way to get more WDW resort guests to head up I-4 than that.
The only semi-practical way I can imagine WDW ever getting (limited) Marvel rights (and lets be clear - its not going to happen - purely an academic discussion) is to make a deal with Universal. As others noted previously in this thread, buying Universal out would be hilariously expensive, so that's out of the question. But, if you could get Universal to sign off on it, maybe you could get an agreement to use some obscure "family" characters which aren't closely connected to the Avengers or other heroes represented at IOA. But again - why, why, why would you want to spend millions building an attraction around a largely unknown superhero which is naturally and obviously going to invite quite unfavorable (if not mocking) comparisons with the well-known characters in Universal's camp.
This is indeed a rather pointless discussion. Nothing wrong with talking about it for those who want to, I suppose, just no point to it. We may as well discuss bringing back Timekeeper to the MK - this time with real time travel.