With Disney acquiring the rights to 20th Century Fox, this gives access for Marvel Studios to have full ownership of Deadpool, X-Men, Fantastic Four as well as other characters like Quicksilver and Scarlet Witch. This also results in Marvel Studios obtaining screen rights for the X-Men to join the MCU and to introduce new villains. With that said, Galactus, one of the iconic villains in the Marvel Cinematic Universe, could be introduced as the new antagonist since the demise of Thanos in Avengers: Endgame.
There isn’t a definite report on where and what movie Galactus would debut in. However, since there are upcoming movies like Captain Marvel 2, Guardians 3, and The Ultimates (where he was a major part of) in the works, it might be possible that he’ll appear in the aforementioned movies as the antagonist.
With such a powerful villain given access to MCU, it is no doubt that Galactus would appear in a movie anytime soon, he could probably be introduced in Phase 5 of MCU. However, it isn’t certain who would play such a strong character yet, but according to We Got This Covered, Marvel Studios has a shortlist of actors who could play as Galactus.
One of the actors in the studio's wish list is Taken star, Liam Neeson. Neeson playing as Galactus hasn't been confirmed yet. In fact, they haven't even contacted Liam Neeson regarding this since this is just the studio’s internal wish list for casting the part, as mentioned, the studio has a list of actors and Neeson clearly isn’t the only one they are looking at to play the part.
There are mixed opinions on Liam Neeson playing the role of Galactus, however, it wouldn’t be bad for a legendary actor such as Liam Neeson to play the iconic villain from Marvel Cinematic Universe.