We know that the Marvel Cinematic universe will include 67 characters who are likely to appear in Avengers Infinity War and Untitled Avengers 4, they are two independent movies without any major inter-linkages. In the first part, Thanos will collect all the mind gems and assemble an Infinity gauntlet, cause a world-wide catastrophe and then in the next part Avengers will unite with Guardians of the Galaxy against the Mad Titan.
Kevin Feige (President, Marvel Studios) has teased the phase 4 of Marvels cinematic universe and is touting it as something never seen before in Marvel films. He said, “I think you look at the comics as a guide, although some titles get rebooted or re-launched, the narrative exist on a never-ending continuum”. What this really mean is if the studio decides to cast someone else in place of an established character, everything that has happened in the past will continue to exist. He is indicating that Marvel may bring Kate Bishop into the cinematic universe as a new Hawkeye in place of Clint Barton (as he may have family issues) or Sam Wilson (The Falcon)/ Bucky Barnes (Winter Soldier) dons the mantle of Captain America, as there are 11 different avatars of the character but it wouldn’t erase the Steve Roger’s past. In this case, Captain Marvel will assume a leadership role in Team Avengers.
He further said that Marvel’s phase 4 will mark a new beginning and a very distinct chapter comprising of the finality of all the previous phases. It would probably include The Inhumans, Black Panther sequel, Captain Marvel sequel, Dr. Strange sequel, Guardians of the galaxy 3 etc. One thing which is absolutely clear looking at the roster of superhero movies in the pipeline is that we will see a huge influx of mysticism and magic in Marvel movies in phase 4. The big villains could be Dormammu, Mephisto who are powerful cosmic villains who can fill the void post-Thanos extinction.