MCU: 8 Theories About Captain Marvel's Role In Avengers 4

6. The Soul World

As confirmed by the director's commentary for Infinity War, that was indeed the Soul World we witnessed young Gamora and Thanos in towards the end of the movie (where she asks what the snap cost him).

With the Soul World, which exists within the Soul Stone, established, it opens up a few possibilities with regards to bringing heroes back, as there's a chance they exist there, rather than being properly dead.

That could mean they can be returned from there too, especially if there's a hero with a connection to the Soul Stone. And while it's never been established yet, since the character hasn't appeared, that could be Captain Marvel. There's certainly potential for her to take on some of Adam Warlock's role from Infinity Gauntlet, which could open the door for her to travel there herself, or there could even be a link to it through the Quantum Realm (which should be linked to Captain Marvel too).

The planet Vormir, meanwhile, which is where the Soul Stone was hidden, exists within Kree space in the comics. And since Captain Marvel has strong links to the Kree - including being half-Kree herself - then there's a chance she knows of its existence and has already come across the Soul Stone, perhaps even helping to hide it there herself.