No one knows exactly which characters are in the contract, but several things can be deduced.
1. lots of characters are not in the contract
2. Characters that became Avengers after the contract was signed have appeared in the park (Dr. Strange)
3. That means that perhaps all characters that joined a family after a date like 1999 are open game (exact date is a guess)
4. Since IOA was built, the standards of a great land have changed. Pandora, Galaxy's Edge, Potter's two lands, New Fantasy Land, and I suspect the new Epic park as well. Even in IOA's park Marvels land is extremely weak compared to the theming used in the other lands.
5. Of course Universal has maintained that area but it can be argued that it does damage to the brand due to cheap theming. Two of the rides are cheap carnival attractions at best, and painted plywood showing a characters use really stretches the inclusion clause.
6. I believe Disney could force Universal to change character depictions to match the latest costume changes and keep them current and in line with the latest publications if they provide new art.
7. Disney knows how much money the characters bring in to Universal and knows that that amount is less than what Universal would currently accept as payment.
8. I doubt Universal likes Disney having their nose in their books, but Disney loves it.
9. The Marvel Branch could create a whole new line or Universe for Disney to Exploit and already has several it could use.
10. There's no way Marvel would have let them have every character so you can bet each family is listed in a clear defined list
So will we see Marvel Characters and rides in the World absolutely. Phase 4 is full of open for use characters and I suspect phase 5 will be as well.
Luke Cage, Iron Fist, Jessica Jones, Daredevil, Blade, Ghost Rider, Dr. Strange, Shang Chi, Guardians, Eternals, New Universe, Kazar, Shield, Adam Warlock, Squadron Supreme, the Champions, The Defenders, The Elders, The Howling Commandos, The Runaways and more to name a few.
It will take time and money to build those brands, but they have already started. You can also bet that they know exactly which characters from in use families they can and can not use.