It sounds very much like one of the most frustrating, unresolved plot threads from the Marvel Cinematic Universe will be resolved in the future. As fans will surely recall, The Mandarin, or a version of the villain, was introduced in Iron Man 3. There's also the terrorist organization the Ten Rings he's associated with, who we met in the first movie in the series. We haven't seen The Mandarin, aka Trevor Slattery, in a movie since. However, according to Marvel Studios President Kevin Feige, that may well change.
Kevin Feige recently did an AMA and answered all sorts of questions relating to the MCU. At one point, a fan asked, very specifically, "are there any plans to incorporate the Ten Rings from the first Iron Man, or the 'real' Mandarin?" To which, Feige simply replied, "Yes." And given the way the question was phrased, this could prove to be a very exciting and interesting development as we speed toward Phase 4 of the MCU. Especially when taking into account the implications of the events of Avengers: Endgame.
Warning: spoilers ahead for Avengers: Endgame. The Mandarin is historically a key Iron Man villain. Unfortunately, Tony Stark gave his life in order to stop Thanos and save the universe at the end of Avengers: Endgame. So that begs the question, how will the real Mandarin and the Ten Rings be incorporated into the MCU moving forward? And more importantly, will this be the version of the character we already know?
Ben Kingsley played the character in Iron Man 3, who turned out to be a washed-up actor simply playing the role of a terrorist supervillain. But in the Marvel One-Shot All Hail the King, we got a look at Trevor Slattery in jail, who was being interviewed by a key member of the Ten Rings. As it turns out, the organization was none too happy that he was posing as The Mandarin, because the real Mandarin was lurking in the shadows. Slattery was broken out of jail to meet the actual man he was impersonating. Thus, somewhere in the MCU, the true leader of the Ten Rings is out there ready to rain destruction upon the world.
With Iron Man out of the picture, we won't get to see that showdown in particular. However, since the MCU has opened in scope a lot since 2013, we could very well see a version of The Mandarin that is more true to the comics, complete with his actual ten rings of power, posing a threat to some of the other heroes in this universe. For now, much of what's coming down the pipeline beyond Spider-Man: Far From Home remains mysterious. But it could include something many of us were hoping to see six years ago. For the full AMA with Kevin Feige, head on over to Reddit.