Story: I'd want them to merge the Snow Queen Quest and SEBEC into one playthrough. With SQQ happening fist then the party going over to save Masao. I'd also want them to let Tadashi write a new scenario for the game following him after he transferred during his 3rd semester
Or what he did during the events of Eternal Punishment. I'd also want Vishnu to have a interaction with Queen Asura if you got him(considering the lore between the Hindu gods and the Asuras). I'd also want them to maybe add Kazuya or a new antagonist who fights the party multiple
times. If ATLUS does their weird adding a new girl thing just make it a VR attendant or something so it doesn't interrupt the story or just don't do it. I'd also like them to add back in cut content like the Time Count encounter(a vessel of Nyarlathotep)
And add some more story content(by Tadashi)
Gameplay: Make Vishnu easier to get considering he's one of the protag's ultimate's. For example they can make him the persona the protag gets if they collect 8+ mirror shards(and the more you get the stronger he is) which would work thematically too with the Asuras vs gods stuff
Make it so you can have all the party but you still have to unlock Reiji with Everyone but Masao and Reiji in the SQQ and then everyone in SEBEC which leads to my next point. No SLs.
If they want to add a interaction system make it like Devil Survivor 1/2 so there's no essential dev locked. With them using this to get Reiji without the convoluted stuff while keeping the theme of reaching out to be his friend but you have to talk to his mom to be able to start
it. I want them to simplify the phys attacks but keep some of the og elementals like Earth and gravity. But otherwise keep it similar to 5's combat without it being so easy. Also add a Nameless and Belladona boss or an Igor one or both. Make everything 3rd person.
Remove random encounters and replace them with a demon roaming around or black/blue/white floating orbs because shadows wouldn't work as those are actual demons.
Graphics/Design: Keep the atmosphere of the og while having P5 graphics level. Use a mixture of the P1 and 2 designs of the characters and not the shitty Kamikaze studios renders(the people who made the JoJo ops)
Music: Make remixed tracks of the og while having options to switch to the og and psp tracks.