If reports are to be believed, Chris Evans is going to return to the Marvel Cinematic Universe as Captain America. However, with Cap's storyline coming to a beautiful conclusion by the end of Avengers: Endgame, it remains uncertain where he would fit in. The Falcon and the Winter Soldier will be addressing the fallout of a world without Steve Rogers, making it fairly clear that the Marvel Cinematic Universe is ready to show what the world would be like after this character is gone.
If Evans returns, it will surely be in a limited capacity -- perhaps a one-off role. Thankfully, with a complex multiverse full of alternate iterations of characters, Evans could return one more time as an alternate version of Captain America, maybe even an evil one. In that sense, it's possible that during the events of Doctor Strange and the Multiverse of Madness, the evil Hydra version of Captain America from Secret Empire finds his way into the main MCU continuity.
Secret Empire
Secret Empire was an event that saw the Red Skull manipulate Kobik, the Cosmic Cube after gaining sentience, into rewriting Captain America's memories, convincing him he was an agent of Hydra from a reality where the organization won World War II. Through Captain America, Hydra then manipulates the entire world, orchestrating a massive takeover of Earth. Ultimately, the Hydra Captain America assembles a Cosmic Cube of his own by gathering fragments throughout the world, only for Falcon and a team of other heroes to use is to restore the original Cap. The story ends with the real Captain America punching out the evil one, restoring peace and order to the planet.
The storyline garnered a great deal of controversy upon its release for taking a character created by Jack Kirby and Joe Simon -- two Jewish men -- and turning him into essentially a Nazi. To make matters worse, at the time, the promotional material for Secret Empire tricked audiences into believing that the evil Captain America wasn't just an evil version of Cap, but was actually a retcon that made Steve evil from his inception.
This felt like a slap in the face for many fans, resulting in many people lashing out at the creative team behind the event. However, in the MCU, Secret Empire has the potential to be done well, especially if Marvel Studios learns from the failings of the previous story and uses the best elements of Hydra Cap in the unique setting of the MCU.
Hydra Cap in the MCU
Obviously, with the Cosmic Cube being replaced in the MCU with the Tesseract, a now-destroyed Infinity Stone, it's impossible to really introduce Hydra Cap the same way. This leaves the only logical way to bring him into the fold being through Doctor Strange and the Multiverse of Madness. This route would immediately solve some of the key complaints about Secret Empire. For one, there would be no illusion that this Captain America is the same Captain America that fans spent years growing to love, which would avoid the sense of betrayal that many felt before Secret Empire.
From there, the question becomes if Hydra will return to the MCU. Depending on how Zemo's plans in The Falcon and The Winter Soldier pan out, it could be that Hydra is already on its way back. However, evil Cap could offer a the organization chance to return behind the man who initially destroyed their ranks.
Captain America's Legacy
Hydra Cap would work great in the current landscape of the MCU to how the franchise deals with the themes of its own legacy. The Falcon and The Winter Soldier, Ironheart, Armor Wars, Spider-Man 3 and Black Panther 2 will all be addressing legacy, touching on how the new generation moves on and grows from what came before.
What an evil Captain America offers is the idea that the MCU would be a very different landscape had certain key events occurred in a different way. This could then lead to the heroes of the universe, including Bucky Barnes and the new Captain America, Sam Wilson, having to face one of their dearest friends in order to stop the rise of Hydra once again.