SPOILER WARNING: Ant-Man and the Wasp spoilers follow for this article. Tread with caution or come back after you've seen the movie.
While Ant-Man and the Wasp saw the addition of a new hero to the MCU in the form of the Wasp (Evangeline Lilly), we also got a new villain to accompany her. Ghost (Hannah John-Kamen) antagonizes the heroes with her phasing powers, but much like the Ant-Man franchise, Marvel takes a unique approach to her villain story. Rather than kill her off or send her to prison, Ghost actually achieves what she wants by the end of the movie and escapes capture. This might actually place Ghost in a really cool position to join a team that the MCU already has the perfect setup for in a future movie: The Thunderbolts.
For those who don't know, the Thunderbolts are a team of supervillains from Marvel Comics. It's easy to compare them to DC's Suicide Squad but the teams are different in some key ways. The Thunderbolts were started by supervillains who decided to pose as superheroes to fill a void that was left after the Avengers and Fantastic Four disappeared. The team planned to gain the public trust until they were treated like the Avengers and would have access to S.H.I.E.L.D. secrets, which they would then sell to the criminal underworld. However, as the public began to see them as heroes, some of the villains began to do so, as well. Ultimately the Thunderbolts had a falling out, but the now-heroic characters stayed on.
Since then, the Thunderbolts have become something of a rehabilitation program for villains seeking redemption. The team has seen a lot of members pass through its ranks, and both Luke Cage and Norman Osborn (who had more nefarious plans) were once leaders of the team. One iteration even had Ghost as a member, which means that there is already some precedent in the comics for the MCU character to join the movie version.
Though there is no explicit setup for the Thunderbolts in the MCU outside of rumors, Ant-Man and the Wasp does a really good of prepping Ghost for the team. Part of what makes this Ghost unique from other MCU villains is that she is portrayed as being redeemable. While Ghost has killed a bunch of people and even seriously considered kidnapping Cassie for leverage, you understand why she's so willing to do these terrible things. Due to her phasing powers, Ghost is always in pain, and by the time the sequel begins, she doesn't have much time left to live. This pushes her to take drastic measures, such as acquiring the Quantum energy needed to stabilize her from Janet van Dyne (Michelle Pfeiffer).
What's important to remember is that Ghost (Hannah John-Kamen) isn't looking to fix her powers so that she can keep on killing people. It's implied she only started doing that because she was trained to do so by S.H.I.E.L.D. until they could find a way to help her, which they never did. Ghost just wants her powers gone, and it's really the pain that drives her to be so ruthless.
Still though, she's made mistakes and done some bad stuff, which means she needs to find redemption. There's no better place for a Marvel villain to find that than on the Thunderbolts! The end credits scene in Ant-Man and the Wasp implies that Ghost still has her powers and is in need of more Quantum energy to stabilize herself. Therefore, she could probably still use her phasing with the Thunderbolts, which would make her a real asset for the team.
The MCU has a few other pieces in place that could lead to the Thunderbolts. In the comics, the team was founded by Baron Zemo, who was evil through and through and wasn't interested in any sincere hero work. Zemo happens to be one of the few MCU villains still alive, as he was arrested at the end of Captain America: Civil War. If the team needs a field leader, the man who pretty much defeated the Avengers by himself would be a good fit.
Thadeus "Thunderbolt" Ross (William Hurt) is another character who could play a big part. The character resurfaced as the Secretary of State in Civil War and even appeared again in Avengers: Infinity War. The character's resurgence could be set up for the Thunderbolts. One possible scenario is that Ross, who has access to the supervillain prison known as the Raft, creates the team as a government-controlled version of the Avengers. He could even name them after his old military nickname, which is too perfect of a fit. Ross is also a leader of a version of the team in the comics as well, though, it was brief. He could also possibly join the team as the Red Hulk, something fans have wanted to see for awhile.
Part of the appeal of Ghost's story is that the heroes end up helping her achieve her goal. She was just a person in pain, but now that she's gotten what she wanted, it's open season! A huge appeal of the MCU is that any character can show up anywhere (within reason) and it makes a lot of sense that if Marvel was going for the Thunderbolts in Phase 4, that Ghost would be a great fit for it.