It seems like every Phase 4 MCU project brings more and more theories about the possibility of a Young Avengers team up and what that would look like in the MCU as we know it. Phase 4 might actually be the perfect time to tell a Young Avengers story because of what they stand for and how many of the members' origins come about. Marvel will likely pull from a few Young Avengers comics to find a storyline for the screen, but no matter which comics run they adapt, a lot of the thematic elements stay the same.
Phase 4 in general has been very focused on legacy, whether that's children dealing with the fallout of their parent's choices and how they interact with their family (like in Shang-Chi) or people taking on new superhero identities to honor those that came before them. This is a perfect place to slot the Young Avengers into, because some of the members' origins actually are about legacy, and it would be a great opportunity to introduce a new, young superhero team in the wake of the disbandment of the original Avengers. The main internal conflict of the Young Avengers story could be their struggle to live up to the greatness of that original team.
Most of the Young Avengers (at least in the original team) are a direct analog of one of the original Avengers, and many of them even have personal connections to those Avengers. Patriot (Eli Bradley) is the Captain America equivalent, which is fitting because he is the grandson of Isaiah Bradley, the first Captain America. Wiccan and Speed, the children of the Scarlet Witch and Vision, have the same powers as Scarlet Witch and Quicksilver respectively. Kate Bishop (the newest Young Avenger addition to the MCU) takes on the mantle of Hawkeye in order to honor Clint Barton and likewise, Cassie Lang joins the Young Avengers with the Ant-Man growing and shrinking powers to honor her father, Scott Lang, who had been killed at this point in the comics.
Since many of these characters have already been introduced to the MCU in some way or another, it's likely that Marvel wants to really focus on the legacy elements of their stories when it comes time to make a Young Avengers TV show or movie. Having the Young Avengers form in a world that has just lost most of its mightiest heroes would be a really interesting starting point, especially when the Young Avengers resemble the original team so much.
It would also be a great way to help audiences move on from the first 3 Phases of the MCU and transition into new team-ups. It's hard to imagine an MCU without many of the main characters that have been present in it for over 10 years, but Marvel wants to tell new stories. The Young Avengers are the perfect way to bridge the gap, giving a sense of something familiar but being totally new and unique and the same time. A team of teenage and young adult superheroes will feel fresh and exciting, and might even be able to transition the MCU into a new age that's just as beloved as the ones that came before it.
A storyline that follows the Young Avengers as they form and struggle with being compared to the team that they're emulating would be really interesting, especially with the familial connections. The world might not be receptive to a new group of superheroes who call themselves the Avengers, especially if they're all kids. The story could be about the Young Avengers proving those people wrong and demonstrating that they're just as capable as the Avengers (after some initial struggle for the sake of an interesting conflict), but also that they're a different team, and perhaps even better in some ways.
Hawkeye is the most that a Young Avenger has been featured so far, and because Kate admires Clint and he has become a mentor figure to her, it's easy to see where the idea of legacy will come into her story. Perhaps at the end of the show, Clint will finally go into retirement for good, and leave the Hawkeye name for Kate to take on, trusting her to uphold what he started, and maybe do it even better.
Ant-Man and the Wasp: Quantumania is set to feature Cassie Lang as a main player, and though Marvel hasn't released anything about the plot yet, the story will probably set Cassie up to be in the Young Avengers and try to be like her father (though hopefully in different circumstances than the comics, with Scott still being alive this time). Eli Bradley's story could be his struggle to live up to his grandfather, and maybe even to be a hero in the shadow of Sam Wilson's Captain America.
There are a lot of different directions that a Young Avengers story could go, but judging by Phase 4's focus on legacy, this seems like the most likely avenue for the teen superheroes to go down. So many of the Young Avengers have direct ties to characters that have already been main players in the MCU, and they'll need to convince the world that they're just as capable as the old team of Avengers. In a much more meta sense, they'll also need to convince fans (especially those who haven't read the Young Avengers comics) to be as on board with this new team as they were with the original one. Focusing on legacy is the perfect way to give the Young Avengers an interesting and realistic conflict, while also staying true to what their stories have always been about.