While DC is scrambling to fast-track a Shazam sequel, Marvel will drag their feet with X-Men...

Yes, a Shazam sequel is being fast-tracked... mostly due to the kids growing... and supposedly, the Black Adam being the most Electrifying Superstar rumor is true. All of this makes a lot of sense. The movie surpassed the expectations of pretty much everyone. The movie was enjoyable, entertaining, and it wasn't loaded with agendas from the cast or Marketing. It was a fun movie that was respectful to the characters (an oddity in the DCEU, thanks to Suck Snyder) but this is just the appetizer...

The main course is the whole Marvel Cinematic Universe phase 4 not including the X-Men or Fantastic Four. I don't trust Feige here... while yes they have to be making plans for characters they actually had at the time like a Black Widow movie, Black Panther, Doctor Strange , Guardians of the Galaxy sequels; that doesn't necessarily mean that they won't sneak in references to the 4 or the X-Men.
I mean...

Generic Kid was turned into Peter Parker... and let's not forget the crazy rewrites that Captain America Civil War have to do in order to fit in Spider-Man... or the recent rewrites in order to add Cap'n Meh Vel to the MCU.

Like say the Guardians could meet a member of the shi'ar like say Gladiator Royal praetor of the shi'ar empire... or in one of those random tasks that they get having to fight off a brood of, uh, well, The Brood.

Or maybe black widow has to fly somewhere and she uses Bushwacker pilot likes a some dude named Benjamin Jacob Grimm?  Perhaps they have to locate someone in madripoor and they pass by the princess bar and Natasha, makes a remark about a past run-in with Patch, the short tempered owner. ( which comic book fans would know as an alias of the short angry stabby Canadian guy who stabbing Canadian guy who ends his sentences with "bub".)

Or maybe having T'Challa deal with a member of the Latverian Embassy who's interested in buying some vibranium for his country.

You know dropping hints of things to come while they figure out how to insert everything in a coherent manner... unlike Danvers.

Hell they could even have background news  playing during scenes. While they main characters are discussing blood orange you could have a TV in the background and have Howard this place only in Fort laud meet and terrorism on the uprising something about the Baxter building or Reed Richards Expedition into the negative zone or something.

But at the same time I kinda get Feige. There's still the sour aftertaste of the recent Fox reboot... personally I think the sooner we wash off the whole Fox era and move on from it as fast as possible the better.

And if Disney was smart they would sneak in like two mini series into their Disney plus service I make it about the Fantastic Four in the X-Men using the same cast that they would use for the movie so they basically have to force people to watch the Disney Plus content order to catch up for the movies.

For example de Fantastic Four series would be at the end episode miniseries and I were each episode basically the first by being the Fantastic for gaining their powers then the season finale would be they coming out as Heroic adventurers and then a Cameo by Samuel L Jackson.
430 villain they could use one of the Lesser Fantastic Four villains like a mole man Puppet Master saving Doctor Doom for the movie. Though Victor Von Doom would appear like in the first episode in a Flashback for establishing the whole Dome Richards rivalry.

For the X-Men I wouldn't go like a whole flashback for all of them I would be using angry stabbing Canadian. I know I say that this before in a random but think about it Wolverine is the only one that you could have a small miniseries kind of like Highlander and it could work.
It will bring miniseries good set up things like Alpha flight or other mutants and even do some background stuff with Cap'n Meh Vel, Ant-Man (Pym), etc.

And last but not least It's  kind of hard to believe that with all these new toys that they're not going to play with them ASAP. My belief is that they're holding back on explaining anything beyond the end of phase 3 until the end of Endgame.  what's the point of getting the X-Men and the Fantastic Four and not use them? Hello phase 4... Fantastic Four... it writes itself!