We’ve Seen This Before
Villains infiltrating every aspect of the government? It sounds awfully similar to the Hydra plot line in Captain America: The Winter Soldier. It would be particularly redundant if Captain Marvel followed a similar path as the Captain America movies. Captain Marvel could introduce the Skrulls and end with her defeating them. Then in the (likely inevitable) Captain Marvel 2, we find out the Skrulls have actually been around all along, and now Carol Danvers has to beat them again. And we have Captain America: The Winter Soldier all over again. Although if it ends up being just as good as Winter Soldier, that may be another story…
Ultimately, it would be nice to see something different. We’ve seen alien invasions in the MCU before. A change of pace is welcome if Phase 4 does something different for the overarching threat. Instead of going extraterrestrial, they could have a threat closer to home. In fact, Phase 4 would be an excellent opportunity to bring Norman Osborn into the MCU.
We’ve seen him done before. But it would be an awesome mix-up to see him introduced as an Avengers villain rather than solely a Spider-Man foe. Spidey can focus on other big bads for his solo movies while Osborn causes trouble for the rest of the heroes. But that’s just my pitch.