I do recall that he enjoyed Persona 5, yes. Especially the menu's UI as if I recall correctly, as it is quite flashy and fluid (quite possibly one of the best looking ones I've ever seen).
I'm presuming you mean Makoto Yuki, the P3 Protagonist, correct? I think he'd be okay, though not as unique as Joker would be of course. I appreciate how much more action-oriented P5 was in comparison to the others, and I think Joker could translate very well to Smash.
He in particular stands out from the other Persona protags in that he not only wields a unique weapon in knives/daggers, but also has a handgun, so he has the potential for built-in projectiles without having to rely on summoning a Persona for them. Plus his "sneaking" animation where he launches on top of the enemy to catch them off guard and then proceed to slice them could work like a Side-B grabbing move, much like Bowser's and Diddy Kong's. Of course, Arsene would have to be part of his moveset, which while not a unique feature among Persona wielders, it is a great looking Persona.
Thinking about the possibilities of Joker's moveset really makes me want him in now; hopefully he'll have a good shot as DLC if Persona Q2 has any potential sway in his favor.