Warning! Spoilers ahead for Marvel's Falcon & The Winter Soldier, episode 6 "One World, One People"
What's next for John Walker after the finale of Marvel's Contessa Valentina Allegra de Fontaine on her offer to work for her, getting a new black and red suit as well as his codename from the comics: U.S. Agent. Here's what that might mean going forward, and where John Walker could pop up next in the MCU.
In Falcon & The Winter Soldier's fifth episode, Sam Wilson and Bucky Barnes forcibly took the shield away from John Walker after he used it to brutally (and publicly) execute one of the Flag-Smashers after the murder of his partner Lemar Hoskins. Furthermore, Walker was stripped of his rank and title by the GRC, who also gave him an other-than-honorable discharge. However, he was later approached by the enigmatic Contessa, who strongly recommended that he work for her. Now, it looks as though Walker did just that after helping Sam and Bucky save the GRC senators from Karli Morgenthau and the other Flag-Smashers near the end of the finale. Gaining his new suit from the Contessa as the U.S Agent, Walker now looks very much like he does in the comics.
As far as when fans can expect to see John Walker again in the MCU, it could be quite soon. The Contessa explained that the new suit and name are due to the fact that "things are about to get weird," necessitating a need not for a Captain America, but for a presumedly darker U.S. Agent that Walker is capable of being. As such, it's possible that the Contessa is building a new team, and Walker certainly seems willing to do whatever the Contessa might ask of him in the near future, meaning that he's most likely going to show up in the MCU projects as well.
It's possible that the Contessa could be meant to first appear in Black Widow before the pandemic created shifts in Marvel Studios' release schedule, so it's possible that she could be a recurring character who pops up from time to time in future projects. John Walker could serve as her primary muscle and enforcer, leading up to this culminating time "when things get weird." Furthermore, it would also make sense for Walker to show up for a second season of Falcon & The Winter Soldier should it happen.
The Contessa is clearly planning and preparing for something big coming down the line in the MCU, and it looks as though John Walker's U.S. Agent is going to be on the front lines whatever it may be. While John Walker has certainly had a tumultuous journey thus far, this last episode confirmed that it is only just beginning. As a result, fans should certainly expect to see the new U.S. Agent soon following the finale of Marvel's Falcon & The Winter Soldier.