Phase 4 will be full of surprises.
The end of the MCU as we know it is almost here. After Avengers 4 is finished, Chris Hemsworth, Chris Evans, and Robert Downey Jr. will no longer be contracted to play Thor, Captain American, and Iron-Man, respectively. It looks like Marvel is positioning Captain Marvel to take over as the main captain, and her movie will include the Skrulls. The shape-shifting aliens play an integral role in the Dark Avengers, a comic book based around villains pretending to be heroes. Now, according to The Hashtag Show, Marvel is developing a script for the Dark Avengers comic.
The Dark Avengers consists of villains who take over after Norman Osborne helps defeat a Skrull invasion. After the regular Avengers are disbanded due to being infiltrated by the Skrulls, the US government awards Osborne a leadership role at S.H.I.E.L.D. for defeating the aliens. He changes S.H.I.E.L.D. to H.A.M.M.E.R. and builds a new Avengers team. The team consists of Mac Gargan (the villain Scorpion, who is taken over by the Venom symbiote) as Spider-Man, Logan's villainous son Daken as Wolverine, Moonstone as Ms. Marvel, Bullseye as Hawkeye, and Osborn as Iron Patriot. The villains pull of several missions before they are discovered to be evil and stopped by the other Marvel heroes.
With the Skrulls entering the MCU, there's a great chance this script comes to life. Since Norman Osborne still belongs to Sony, Disney will most likely work on a joint deal to bring another Spidey foe into the MCU as they did with Vulture and Scorpion in Spider-Man: Homecoming. It's also worth noting that Marvel has many scripts commissioned for their hundred of characters, with most of the ideas landing in the garbage.