I think that now that MCU has almost triplicated the quantity of projects they produce in a year, we will have different storylines completely different from each other before they all lead to a single event, in which I think could be an adaptation of Marvel’s Secret Wars and Annihilation in an Avengers trilogy.
I think that while we wait for the big crossover between the projects, we would see three different sagas, in which each one would be divided in two parts:
The first one, in Earth:
First part (street saga): with Daredevil Jessica Jones, and other defenders, trying to defeat Kingpin who would be trying to rule New York.
Second part (political saga): the Thunderbilts will be created and will fight crime in government’s order. They would ignore some problems and mess up other ones, so the Avengers in Earth, like Captain America, Joaquin Torres, Patriot, Rhodes, She-Hulk, Hulk would need to interfere.
The second one, between the galaxies:
First part (extraterrestrial conflicts): with Ms. Marvel, Photon, Captain Marvel, Nick Fury and SWORD, trying to solve conflicts out of Earth. The Kree-Skrull war could be explored.
Second part (cosmic saga): with the introduction of new gods, cosmic entities that will end up with introducing us Galactus. The heroes involved in that saga could be the Guardians of the Galaxy, Eternals, Thor and others that could yet be introduced like the Silver Surfer. This saga could hint about Galactus arrival in the future.
The third one, that will explore the multiverse;
First part (Incursions saga): with Doctor Strange, Ms. Marvel Clea and other sorceres exploring the multiverse and fixing incursions. The concept of incursions could get further explored because it will be important for the future Secret Wars movie.
Second part (time travel saga): This saga could be tied to the multiversal one, continuing the plot line of Loki series, with the introduction of Kang and his relationship to the Quantum Realm, that could be explored in Ant-Man Quantumania. The Young Avengers and the Fantastic Four could have a role to play on this saga.
We could also have the introduction or a mention of Doctor Doom in Black Panther Wakanda Forever, besides being the main antagonist in a Children’s Crusade movie, but I don’t know in which saga these movies could fit in (maybe he could be a villain from the political saga in which the avengers and the thunderbolts would have to join themselves to defeat him). Doom could be very important for a future crossover.
The crossover could be an Avengers trilogy and I will write my theory about each one of them:
Avengers 5 (Multiversal War): The first movie could have the main antagonist as Kang, from the multiversal saga, who would fight his variants across the multiverse to destroy their universes causing incursions. The avengers would have to defeat Kang and stop the incursions, but they wouldn’t be able to fix the last incursion between their universe and the ultimate universe that could be explored in future marvel projects. At the ending of the movie, when the two universes are colliding, Doctor Doom (who would have already been introduced as a villain in the MCU) would use his powers to create a whole new universe in the void, where he would rule everything and all the main locations from the multiverse would be, like the Battleworld from the comics.
Avengers 6 (Battleworld): This movie would explore Battleworld, a world where Doom rules. All the heroes would be obeying him, and would think he is good, because they wouldn’t remember their past in the original multiverse. Somehow the heroes could discover the truth and defeat Doom, creating their universe again.
Avengers 7 (Anihilation): This new universe would contain people from across the multiverse and would have a lot more people than resources. That would be funny and ironic, because the heroes would have to solve the problem Thanos was talking about in the past avengers movies. They would have to find a way to do so, and it can’t be the same way thanos wanted to do it. At this point we would know better about cosmic entities and how they works, so the heroes would know that they need to do it fast, because if not, the cosmic entities would do so, to find balance. I think that in the MCU, the cosmic entities could be the ones who control everything in a universe, and to do so, they have celestials that keep the balance in their way. We were introduced to some of them in Eternals, and I think that we will be introduced to the most powerful one: Galactus. He would be a celestial that eats planets. As Earth would be full of people, that would be his next target.