10 Big Changes The MCU Could Introduce In Phase 4
9. X-Men And Fantastic Four Join The MCU

A plethora of classic heroes and villains will come roaring back to Marvel Studios when Disney crosses the Ts and dots the lower-case Js in its 21st Century Fox acquisition, chief among them the X-Men and the Fantastic Four.
Phase 4 seems as good a time as any to integrate these characters into the series, and Marvel might even be sowing the seeds for this right now. Phase 3's Captain Marvel could serve as a bridge between the MCU and the Fox franchises.
Not only will Marvel Studios' first female-led film introduce the Skrulls - an alien race with deep connections to the Fantastic Four - the fact large portions of it will likely be set in space creates the opportunity to connect it with upcoming X-Men sequel Dark Phoenix, which will also take place up in the cosmos.
Whether Marvel will take steps to tie the characters it's inheriting to the MCU so soon remains to be seen, but there will be other opportunities to do so in Phase 4.