Hello there! sorry if this is a bother but do you still know anything else about atlusxp5? i've been digging as of recently
Sorry it took a bit to respond (was away on vacay). Funny you should say that, I recently looked at their channel to see if they've updated since their last teaser from 4 years ago TT0TT (spoiler: they have not)
What I know about it (from memory). Prior to P5 ever having a speck of actual confirmation on the internet, someone decided to make a fan P5 project called "Persona 5 Imagining Project/P5IP" and it was "by" AtlusxP5 (link to channel). They posted some cool songs (that aren't original, they are copyrighted, but still awesome), some character sheets (possibly on twitter? I don't know much about that side, sadly it's defunct ;w;), and trailers, and people analyzed it on the now defunct Atlus Forums/Threads
I think Atlus struck them down (or they had to priv their videos at least for a good while, and their twitter's gone so....who knows what happened tbh) and.....well.....we don't know what's up anymore. TT0TT
Thankfully, a lot was saved/salvaged by the lovely trifectamix, who has all the songs iirc as well as pics of the char sheets and threads. I highly recommend them! They did a great job preserving an amazing period piece of Persona fandom!
If you wish you had more of a fix....well good news, another fan creator (Assinine Syndrome) wanted to continue the saga. Or at least, write a fanfic-type posts about what they think would've happened. Most of the writing are in the video descriptions iirc. But they follow a similar format of existing songs (and remixing/mashing them up), and I recommend them! They finished their version of P5IP and have gone onto their own fan music list of P6 VERGS (and seem to have a P7 concept in the works).
Here's Assinine Syndrome's channel (where the meat of it all is), and here's their fanfic page, they only did like a prologue chapter to P5IP/P6V but it might still be notable to read if you're interested.
(note in case I've confused anyone: AS isn't AtlusxP5, I believe they are just a big fan of P5IP is all, but they're stuff is fun too and I recommend them).