MCU: 8 Theories About Captain Marvel's Role In Avengers 4
7. Setting Up A Skrull Invasion
As mentioned, Captain Marvel will feature the war between the Kree and the Skrulls, with the conflict expected to have a key role in the solo movie and Carol Danvers heavily involved in it.
That, however, may just be the first part of a grander plan for the movie, which could move forwards even more with Avengers 4. While it'll be the end of the MCU as we know it, Kevin Feige and co are constantly looking forwards, so the movie has to setup the future as much as it celebrates the past.
A good way to do that, then, is to plant the seeds for their next big story arc, which could be Secret Invasion - where it's revealed the Skrulls have long infiltrated Earth, and that a hero themselves could even be one of them. With Captain Marvel's involvement with the species, and her knowledge, then she'd be a good viewpoint for the audience to see this happening, and perhaps her involvement could even be what sparks it all off.