Marvel Studios doesn't plan to announce too much of the Phase 4 slate after Avengers: Endgame at the same time. The Marvel Cinematic Universe has continued to produce films every year since 2008, making it one of the most active and successful franchises in history. After taking things slow to start, they made a huge announcement in the fall of 2014 that outlined the MCU's future all the way until 2019.
With the long lead time of this slate, the plan has shifted in several ways, and mostly for the better. The original Phase 3 slate didn't include Spider-Man: Homecoming or Ant-Man and the Wasp, and the additions of both meant the wait for others became slightly longer. However, it also changed with the removal of Inhumans, which originally would've bridged the gap between Avengers: Infinity War and Avengers: Endgame. Officially, Marvel is remaining tight-lipped on the MCU's future after the end of Phase 3, as only Sony's Spider-Man: Far From Home has been announced. Unofficial signings and reports have given us a decent understanding of what the next few years will look like, but it sounds like MCU fans shouldn't anticipate a full Phase 4 announcement at any point.
Speaking with Comicbook, Marvel Studios president Kevin Feige was asked about the MCU's future and any potential plans to announce what is coming next. He confirmed once again that they won't announce anything until after Avengers: Endgame and likely even Spider-Man: Far From Home. They already know what the future is, but any announcement of the future will be much smaller. He said, "I don't think we'll be announcing five or six years, but we know sort of where we want to head in the next five or six years."
As much credit as Feige and Marvel Studios receive for largely sticking to the slate they announced five years ago, not doing a similar announcement is understandable. Any slate reveal gives fans certain expectations for when a film is set to come out and can even show how the next big event could be built up. Instead, they appear ready to go back to their approach in the earlier years of the MCU and just announce a few years of films at a time. So, when Marvel Studios does confirm some future films later this year, they may just focus on the next two or three years to start.
Feige has also previously mentioned that he isn't even sure if Phases will continue after Avengers: Endgame. They may have a general plan for what the future can hold, but moving away from a set structure should give them more freedom in telling these multiple stories. Plus, not announcing a major five-year plan could be even more beneficial for Marvel Studios right now as they'll soon have access to the X-Men and Fantastic Four characters once the Fox-Disney deal closes.
If their future announcement this year confirms Black Widow and The Eternals for 2020 and Black Panther 2, Doctor Strange 2, and Shang-Chi for 2021, that will give audiences a great understanding of where the universe is heading. But, this limited window also means they can announce plans for their new characters for as soon as 2022 without worrying about changing the slate that was already announced. We'll have to wait and see exactly how Marvel Studios handles this future announcement though, and in what state Avengers: Endgame leaves the MCU in for the future.