Just lots of thoughts after Endgame:
Phase 4 should introduce Doom early and obviously not kill him as he'll be the brains behind a lot of stuff. At the end of Phase 4 Galactus or something else massive is the threat, and Doom will show up to help. He lives on earth also, so he's invested in saving the planet.
A good portion of the movie is Doom shit talking the heroes about how foolish they are and none of this would have happened if they only had the intellect to see the vision behind his plans. Also they can't do shit about it because they do need his brains to defeat Galactus.
No more Time Stone: Dormammu isn't going to be a problem if he's anything like the comics (In his first fight with Dr. Strange, other creatures started to invade Dormammu's realm. Dr. Strange stepped in to help when it was clear Dormammu was going to lose. After the battle Dormammu was pissed because he had a code of honor where he wouldn't kill Dr. Strange after getting his help). Basically, a deal is a deal, and early comics Dormammu isn't going to go back on his word even if the time stone isn't on Earth anymore.
However, Dr. Strange 2 would be cool if all manner of vicious things are looking to grab earth now that the Sorcerer Supreme no longer has the time stone.
Black Widow movie: It's a last movie for Romanov, and an origin story for a new Black Widow. Takes place during the 5 years after the snap. Romanov secretly trains some women to be her successor, determined to make sure they won't fail like she did against Thanos.
She sends them away on their final mission, keeping them in the dark about her going with the Avengers in Endgame. They infiltrate the facility easily, but Hulk undoes the snap on the other side of the world. Suddenly there's a shit load more guards than when they came in. Two of the three die while escaping, and the last one comes back to a recorded message from Romanov. She's approached by Fury and works with him as she takes the mantle as the new Black Widow.
She shows up in other Phase 4 MCU movies like Romanov did, and it'll be a nice touch that the audience knows her background, but she's a mystery to the other heroes.