It seems they added an NPC in Escapade that, for some strange reason, get's a portrait on the last days you can go around doing stuff in the city (3/3 and 3/4, I believe) and one of things he says is highlighted in red text. This is from some guy at another forum, but I thought it'd be cool to share:
 
 

I've heard people guessing that he's going to be a character in P5, or another Atlus game.

Oh yeah that dude. I haven't talked to him much nor did I get the chance to see his portrait but he's definitely more interactable then your average NPC. I'm not entirely sure why he's there. I dunno, he's quite intriguing though I'll give him that.

O.O maybe he'll be the next MC... that would be sweet...
 
I like the look of him, and he smokes and knocks up peeps XD

Man, I was really hoping that was just a long setup and when you posted the picture it'd be Adachi or something.

Interesting, truly.  Kind of reminds me of a younger version of this guy from Trauma Team: 

" Interesting, truly.  Kind of reminds me of a younger version of this guy from Trauma Team: 

 Gabriel Cunningham, the character I posted from Trauma Team developed by Atlus, also has a son and a failing marriage.  Kind of links with the "Man Drinking Alone's" possible story. "

I should probably get P3P. That'd be pretty cool if he did have something to do with the next Persona game. Maybe he's actually a primary character after the events of the game, i.e. he knocks up his girlfriend and cheats on her during the game.

Apparently, dude's called Vincent (from GameFaqs, copied from NeoGAF):
 

" That Vincent talks about dreams so much might give a hint that P5 is going to have something to do with dreams and dream psychology. "

Have they given what year Trauma Team takes place?  Keep in mind that P3P released in Japan last fall while Trauma Team was just released there last month so it would make sense for Atlus to stick him in there.

Forgive my twisted teenage mind but... 
 

...Man, I really unloaded on you.    

You can deffinatly see his portrait before the last couple days, I saw his portrait in early january.

As someone said on GameSpot: (Nexus_Nocturnal)
 
 

The red text is "nothing to do with your problems."

He says this after asking if the dreams he has been having have anything to do with him betraying his girlfriend.

I hope he is the MC in a new MegaTen game. His nightmares he is talking about could be like a dream world. Perhaps that's going to be P5's "Dark Hour" or "TV World".
 

" @Catolf:   Yeah.  It'd be cool if this character is a preview of what's to come in Persona 5.  I'm eager to see what Atlus actually has in store along those lines. "

I was thinking Trauma Team reference, but if the dude's name is Vincent, it seems more likely a Persona 5 reference. The nods towards dreams could definitely be a key to the plot of the game.
 
"Nothing to do with your problems," huh? Wonder if that's just referencing the fact that none of the Persona game stories are really connected in any way, or if it has some deeper hidden meaning?

For the record, guys, you can go through all of his dialogue significantly sooner than the last few days of the game. The only reason most people think that is that the club owner mentions him in passing while you're talking to him about the monk in that end-game phase where you're wrapping up Social Links. However, having finished the game myself, I believe he shows up as early as September and you can go through the entirety of his dialogue in two separate nights that month. He doesn't go on to say anything new in March if you manage to accomplish that and I recall getting his portrait to show up before that.
 
I think I read somewhere in that main GameFAQs thread that supposedly people had concluded elsewhere the guy was a cameo character from an existing Atlus game based on the scans of the Famitsu preview of P3P. I can't seem to find any evidence that supports that in English or Japanese, though. Based on some searches of Japanese forums I conducted, though, it seems as though people have reached a similar consensus that he probably has something to do with Persona 5, although some people contend he might be Trauma Team's Gabe. I'm more inclined to think it's the former, mostly because Atlus doesn't usually do cross-franchise cameos with its games; the ones I can think of that happen in SMT games are of characters from other existing SMT series to begin with.
 
If anybody wants me to, though, I can do some digging around in the ISO when I have free time. There probably isn't much else beyond what people already found with stuff like that hex editor, but having gone through Persona 3 and 4's file systems in the past, I do know Atlus has a weird knack for leaving around obscure and unused content in its game discs. Most of the important stuff isn't really all that encrypted and what still is can be handled pretty easily with third party programs, from what I recall.

he wont be the mc. he's not in high school

Though there is a visual similarity between the characters, I doubt that Vincent is supposed to be Gabe.  Otherwise, why would he be referred to as Vincent in the code?  (Though hell, Vincent could be Gabe's middle name, for all we know.)

" he wont be the mc. he's not in high school "

" @FluxWaveZ: P2:IS deals with shadow selves in a very similar way to P4 "

" @slyspider said:

" he wont be the mc. he's not in high school "

That and he seems to have a little too much backstory to be our next Charlie.  I imagine he is from Persona 5 though, maybe the main character will be his child in the game or he's an early victim of whatever happens in the falling dream (perhaps it's P5's equivalent of being left in the TV world when the fog clears). "Nothing to do with your problems" probably refers to the fact that he's dealing with a completely different shadow-related problem, note the red Zelda text.  Of course, this is all just speculation. "

Well the plot certainly thickened since I last came here. I'm still not sure what to think about this guy. It does sound P5 related but at the same time it feels a little too soon? Ugh. Come on Atlus, give us something!

" he wont be the mc. he's not in high school "

Oh, I like this. I like this a lot.

I gave him a character page, seeing as he doesn't appear to have one.

" It does sound P5 related but at the same time it feels a little too soon? "

" @FlipperDesert: As you may or may not have noticed already, chapter two has already been posted for your reading pleasure. Unfortunately, there is a distinct lack of both Funky Student and Mysterious Fox, both of whom I originally planned but couldn't quite work into the current plot arc yet. While I don't want to give away future developments of the story, it's possible that they could show up as important characters later on in the story. "

" @eroticfishcake said:

" It does sound P5 related but at the same time it feels a little too soon? "

You do realize Persona 4 got released 2 years ago, right? "

" @Pepsiman: I agree that its a small possibility, but they may have made some early art and then aged Gabe later and decided to put the younger Gabe art in P3P.  All this assumes Trauma team takes place in like 2015, I don't know if that's true or not.   And character names change all the time so a "Vincent" changing to Gabe later isn't that big of a deal.   But the eye color looks different to me and if it was promoting Trauma Team you'd think there would have been more official confirmation since the games are now out in both Japan and the US. "

" @slyspider said:

" he wont be the mc. he's not in high school "

That and he seems to have a little too much backstory to be our next Charlie.  I imagine he is from Persona 5 though, maybe the main character will be his child in the game or he's an early victim of whatever happens in the falling dream (perhaps it's P5's equivalent of being left in the TV world when the fog clears). "Nothing to do with your problems" probably refers to the fact that he's dealing with a completely different shadow-related problem, note the red Zelda text.  Of course, this is all just speculation. "

The concept of dreams/falling definitely sounds like it would be an awesome Persona theme, so I'm hoping for that!
 
As for the theory about Gabe, I'unno -- honestly, I see more differences over similarities. If you wanted to stretch it a little, the dates kiiiind of line up -- Trauma Team takes place sometime after 2021 (since Second Opinion is dated around 2021), P3P ends in 2010, and Gabe's son, Joshua,  is 10 if I remember correctly -- but really? I think that's all a coincidence. He just doesn't come off as how Gabe does, and his appearance differs quite a bit, as many other people pointed out.

Persona: Inception.

" Persona: Inception. "