Yesterday, it was revealed by Deadline that Chris Evans was nearing a deal to reprise Steve Rogers aka Captain America in a small supporting role (similar to Robert Downey Jr. in Spider-Man: Homecoming) for an undisclosed MCU project. They also mention Evans might be returning for second thing, possibly a film but didn’t reveal what that could be either.
There are a couple of obvious options such as old Steve Rogers becoming a mentor to Sam Wilson in Captain America 4 as he takes over the mantle. Also, seeing what Steve was up to while hiding between Captain America: Civil War to Avengers: Infinity War, not unlike where Black Widow takes place in the MCU timeline. There is the multiple years between Avengers: Infinity War and Avengers: Endgame, I’m sure there would still be threats in the wake of Thanos’ snap.

There is another option to add. Thanks to Avengers: Endgame, that Steve was able to go back in time to be with Peggy Carter and stayed there starting in 1948 just when The Cold War begins. Steve as an old man ends up handing Sam Wilson the shield at the end of the film and launching the events that will be covered in The Falcon & The Winter Soldier.
The Multiverse also opens the door to other timelines allowing to them return to WWII.

I think it’s hard to imagine with all the threats surrounding him during that timeline and Peggy Carter’s work at S.H.I.E.L.D. that he doesn’t eventually jump back into the fray between his return and Avengers: Endgame. What would make a lot of sense would be Rogers leading his own team which has previously happened with The Invaders, a group mostly made up of WWII era heroes such as Namor McKenzie aka The Sub-Mariner, Union Jack, Spitfire, the original android version of The Human Torch aka Jim Hammond, Blazing Skull, and multiple other wartime heroes that could get some live-action love.

It’s worth noting that Wyatt Russell’s John Walker aka U.S. Agent, Anthony Mackie’s Sam Wilson, and Sebastian Stan’s Bucky Barnes have been established members on the roster.

There is another superhero that was kicking around during WWII and The Cold War that has teamed-up with Captain America the comics that could make for another excellent addition to those ranks, that being the Canadian super-soldier Wolverine.
Luckily, since Logan doesn’t really age he can be able to time-hop to various eras of the MCU including something like WWII or even futuristic setting like with Old Man Logan.
Rebooting Wolverine is clearly a huge priority to the studio alongside the X-Men and having the anti-hero connect to various MCU characters beforehand wouldn’t be shocking since he’s, like Steve Rogers, he is part of a super-soldier program via Weapon. When his origin takes places in the MCU doesn’t seem to be set in stone and Marvel can certainly tinker with it to fit their needs but I’d personally like to see him running around WWII without his indestructible skeleton and then get it during The Cold War.
It might be a good idea to introduce Wolverine as a supporting character elsewhere so that he doesn’t dominate the main X-Men films as much. The fictional X-Men locale of Madripoor is going to be introduced in The Falcon & The Winter Soldier, which had many fans jump to conclusions that Wolverine is connected to the Disney+ series, although, there hasn’t been credible information backing up these fan desires. However, it becoming a stomping ground for the mutant eventually wouldn’t a surprise.
If they’re genuinely going to bring Chris Evans back I think it is worth considering giving him another period project since while Captain America: The First Avenger canonically takes place during WWII, it felt like they copped-out by limiting how much fighting he did against the actual Axis. The Cold War era could be another fine option as Steve combating the new threat of The Soviet Union during the height of the nuclear arms race feels just as a plausible of a setting for another adventure.
X-Men villain Omega Red could be a good baddie to use as well given his connections to Soviet Union super-soldier experiments.
It’s worth mentioning we’ve previously seen Easter Eggs to canonical members of The Invaders lineup in previous Marvel Studios films.

Union Jack was teased via Iron Man 2 as Joey Chapman was listed as one of the racers going head-to-head with Tony Stark. The Human Torch is seen encased in glass and Namor’s Atlantis was briefly teased in Captain America: The First Avenger at the Stark Expo (blink and you’ll miss the underwater city nod). The S.H.I.E.L.D. boat called The Lemurian Star in Captain America: The Winter Soldier is a direct nod to Namor villains The Lemurians, a sign that something nefarious was happening onboard.
I’m sure we’ll start to get confirmation what Evans is actually going to show up in but I think fans are also quite comfortable leaving old Rogers alone as well given his satisfying ending.