At least in the foreseeable future I can't see Disney thinking about buying out Universal Orlando on Marvel..it's kind of a win-win for them. True they aren't able to utilize opportunities with a company they own in their number one destination but they continue to get money out of it.
I'm sure they expected the whole Star Wars revival to get them at least decent money (I doubt they thought it would be this big of a money maker but still) in return for the purchase price over time and they get to keep people interested in the series for some years and then add on the new land which will likely bring a good number of people to WDW.
Vice versa I can't see in the foreseeable future Universal thinking about releasing themselves from the contract-it's a win-win for them as well. Yes their HP is doing fantastic but the Hulk and Spider-man are huge drawls to the park as well. With Universal, even with adding a new attraction every year til I believe 2020, they still would probably like to keep the above two especially since to many people who I see comments about on this site and other review sites the rest of the parks are lacking or losing their appeal (that's not necessarily my opinion though of Universal Orlando).
Something to consider about Disney is they just recently made AMC Theatres (and perhaps others), which is currently headquartered right near me and is the only theater company I prefer to go to, completely change their pre-purchased discount tickets. They used to be gold (new releases) and silver (non-new releases and which were discontinued over a year ago) which had very few film distribution limitations.
Now they have red and green passes with the following stipulation: "Green and Red Tickets are valid for one admission to any movie except those distributed by The Walt Disney Company, including, but not limited to Disney, Pixar, marvel and Lucasfilm, Ltd. titles. These tickets EXCLUDE ALL Disney movies including: ANT-MAN, BRIDGE OF SPIES, THE GOOD DINOSAUR, STAR WARS: THE FORCE AWAKENS, THE FINEST HOURS, ZOOTOPIA, THE JUNGLE BOOK, CAPTAIN AMERICA: CIVIL WAR, ALICE IN WONDERLAND: THROUGH THE LOOKING GLASS, and FINDING DORY." This is very unfortunate to my husband and I as we haven't really paid full price for AMC tickets for years because he used to get them at work and the company I used to work for also had them. His work and my previous company stopped carrying the new passes due to the huge limitation thus not worth the cost of buying the tickets in bulk. The obvious money making ones are Star Wars and Marvel. It would appear that Disney is trying to maintain a tight control over Marvel in other ways, even as trival as it seems to control discount movie tickets, aside from Universal Orlando.
As for other lands I may be in the minority but I'm not really enamored with a Cars land at WDW. Sometimes it works out to have separate themes at DLR and WDW. As far as I understand the DLR's version of Test Track is Radiator Springs Racers. I would be more inclined to like Monsters Inc or even a mixture of Pixar-related themes.