Yeah, assuming the video is true and the dialogue is an actual script for the movie, it sounds like they're gonna try to turn her into the character Mysterio was promoted to be in Spider-Man: FFH; someone from another universe instead of someone from a different dimension. Although I guess they could always say that she IS originally from another dimension, but she was just living in a different universe after she lost her home (we know that this is canon in the comics, with America travelling to universes other than the 616 one). She DOES mention that she is a orphan in the video, which is comics accurate. So hopefully at least her moms aren't getting erased.
I have a really bad feeling about her being deaged. Like you said, it feels like a cop-out. I mean, yeah, she would grow up quicker in that universe since the MCU actually takes place in real time, but it's just a weird decision if we consider her dynamic with the Young Avengers. Her relationship with the team, specially Kate, will have to be entirely different if she is that young in the MCU. She would be like the Molly Hayes of the team, which is sooo weird to me. AmeriKate definitely won't be allowed to flirt or make jokes about sexuality, which sucks. Which makes me question something I would rather not think about
: maybe they're not planning on using her with the Young Avengers, after all. Maybe they're just seeing her as a completely individual character for an individual role. That's a really disappointing possibility to me, because MAC was such a good addition to the team in the comics, and seeing the MCU basically write her out of the team like this would blow.
And now I'm getting worried about which other liberties they might take with other members of the team. And how that might affect the comics and other media. Oh, lord...
I'm just confused as to why they would need to wait for her to age into her comic book self when they clearly didn't feel the need to do that with other teen heroes like Peter, Kamala and Kate... Like, what's the reason why America just can't be her more mature self from the beginning? It's weird.