Very interesting. Been seeing stories/studies like this for years now, but time accelerates trends these days.
I think it depends in part on specific regions and demographics - and it might change if there's less 'going away to college' or if all media gets 'neutral accent' w/ A.I. newsreaders, etc. Meanwhile, I've noticed, in Florida at least, both packets of really strong/entrenched local accents, blending with others (same age group) in some cases, in other cases not. And (I wrote about this in the stone age, reference by request) where/how one works also impacts language (like "legalese" vs. teaching vs. farming/construction) etc. Anyway, demographic trends go deep and in tributaries, but yeah, this is interesting!

The talking heads on the news have been getting their regional accents beaten out of them for decades now... I'm not sure AI would be any more flavorless 🫤

People rarely comment on my 'accent' but if they do, it's "oh, you're from New York", or "tri-state" (once upon a time). My usual answer was, "I don't have ANY accent... I speak the standard television dialect coming from the networks".
OTOH, like a mockingbird or chameleon, I've gotten good at 'blending' when useful.

Mine tends to shift. In NY, I'm a New Yawker, in the south, I get a drawl, in England, I became British. I have a cousin who grew up in NJ, moved to GA, and she now has a full time drawl.

I have a mild drawl by osmosis. My people were alllllll Appalachian.

Funny story time. When I was 9, I stopped talking, because I stuttered. The school district couldn't have that and put me on the district's speech therapist's schedule. Ever since, I sound like I'm from Maine (though the accent has drifted south to Boston over the years). The therapist was from Maine. I've never been in Maine. And I didn't go to Boston till I was 40.