Now that Kang The Conqueror is no more...
Doctor Doom will take its place for Phase 4 starting with Fantastic Four. I feel like Galactus will have something to do with bringing the 4 into the rest of the MCU. Right now the MCU is in the 7th cosmos so I assume eventually Reed Richards will save the day along with Doctor Doom and Molecue Man if they go the Beyonder route. But first, Doctor Doom must be the villain. I am surprised they showed Galactus first before showing his herald Silver Surfer.
The whole MCU hierarchy can be confusing on who's the strongest since we're heading into cosmic being entities before the abstract come into play.