Junpei, Shinkiro, and Yukari are all my personal favs to get into this game.Mainly because I think they would work so damn well. I would love to see DLC outfits.
Mitsuru and Akihiko in their school outfit(s).
I’d love to see Adachi in it, especially if they’d expand the story since I’d like to see if that crazy guy could still keep his promise of abiding by the law,
granted they’d have to find an excuse to get him out of jail. He could be that crazy, but oh-so-entertaining teammate of questionable moral standing.
Though if he was announced I’d be a bit worried that he’d be the Akuma to Yu’s Ryu since his persona is an evil Izanagi.
I had a dream last night that Jimenez from SMT: SJ was a DLC character. Here he had undergone a Kirijo Group Experiment to fuse a man with a Shadow. It was cool, he did not have a Persona Gauge.
Damn impossibilities. Somewhat realistically, I would adore Junpei.
I think the character roster is solid. Still, I would like to see some more antagonists. Takaya, Ryoji, and Adachi would fit perfectly with the rest of the cast, as long as their apperances make sense of course.
Also:
Make it happen.
To be fair, all the persona games are in the same world, so it’s not entirely *impossible *that p1 or p2 characters make an appearance.
I’d assume they’d be much older now, though. Raidou is making appearances everywhere, so what the hell, but that doesn’t give him a persona and well… Yeah, SMT period has no place. No real link to the series, but it could be done. SMT Nocturne was full of discussion on dimensional rifts and alternate universes, so it’s not entirely uncommon to see other series faces appearing. It’s simply… where would they get their personas?
And only people I can see having anything remotely similar are the characters from devil survivor series, which means summoning a certain demon from their COMPs. Same with older Devil Summoner/SMT characters (Or SMT:Strange Journey.)
TBH, I would much rather have characters from other ArcSys games than characters from other SMT games. They can be used as advertisement for the upcoming BB and GG port. Carl Glover totally plays like a Persona character anyway so why not?
I think adding Hitler as a playable character would give this game all the publicity it would ever need.
Margaret and …
Spoilers for Persona 4
Spoiler
Adachi
Spoiler
Mentioning Adachi’s name as a DLC character is a pretty major spoiler…it would ruin the whole P4 game if I knew it before playing
fixed emil.
I want to see some non-canon stuff like just give Dojima a Heirophant persona and build him a fighting style from scratch, same could be done for the other arcanas ya know. Throw Sayako in there and give this game it’s own Valentine lol. She has the Devil arcana so there should be some good personas to choose from.
They should definitely try to atleast fill up all the cards of the tarot, we’re missing Moon, Heirophant, Devil, Tower, Strength, Aeon, Hanged Man, Lovers, Justice, Temperance, Sun
They shouldn’t have put two Fools, Emperors and 3 Fortunes…
Needs more Universe arcana 
All her attacks involve just staring at you with a blank expression
Well to be fair the protagonist is always Fool, so it makes sense to have two (though Aigis was something else in P3vanilla), and 2 of the three fortunes are the same person.