After testing the feature in a time-limited event called Tachyon Anomaly, Marvel's Avengers will let multiple players in the same team play the same hero permanently as of its next update.
Square Enix detailed this and other upcoming changes to the live-service beat-em-up in a Roadmap update for July (opens in new tab): "Finally, due to your feedback, we're permanently turning on the ability to play multiple of the same Hero during matchmaking and when forming Strike Teams." If you ever played Marvel Heroes and enjoyed seeing three Hulks running around together, you'll get a kick out of that.
Also coming in July is Omega-Level Threat: Family Reunion, which Square Enix calls "our toughest content to date… which culminates in a chaotic fight against the Super-Adaptoid – this time, with astonishing new abilities." Multiplayer mega hives are getting harder too, but will be faster to complete because the amount of heroic gauntlets needed will be cut in half.
Beyond that, there's the War for Wakanda expansion planned for August, which will come with the addition of Black Panther as a playable hero, new villains including Klaw, and costumes inspired by the Marvel movies.