Persona 5 was a momentous JRPG, not just for its own franchise, but the genre as a whole. The shear style of the game and its character stories helped sell players on the niche turn-based combat and mechanics. That being said, it's the Persona game that spent the most time in development for a number of reasons. Now the next game is presumably in development with Atlus and P-Studio, and with the huge success of Persona 5, the scale and scope of the next Persona game could be even bigger.
However, that extra ambition could prove problematic for a game like Persona 5, which strode a very delicate line between mechanical complexity and narrative pacing. The next Persona game would have to be in development for next-gen consoles at this point, considering the PS5 and Xbox Series X are out this holiday. That means there's a ton more horsepower to work with, in terms of graphical fidelity and processing. Persona 5 marked a huge step forward for the franchise, but a potential Persona 6 may take things a step further.
Persona Games Are Long, Very Long
Obviously taking things a step further isn't always a bad thing, but for Persona, that could equate to an even longer amount of time spent in the game. Of course, nobody wants to complain about fans getting as much value as they can from games, but extending the playthrough of a Persona game is a tough ask. Persona games, even on their base releases without extra content, typically clock in at about 100 hours of playtime to completion. Persona 5 Royal in particular, on average, takes around 130 hours with the third semester unlocked. Persona 4 Golden has a similar playtime of around 100 hours.
Nothing wrong with a long JRPG. In fact, that's typically the draw with games like Persona or Dragon Quest. Persona in particular has become well known for having long playthroughs ever since Persona 3 modernized the franchise into its current framework. Persona games are all about balancing this JRPG version of a work/life balance. Characters spend their normal days in high school being an honest student and exercising their social freedoms after class, whilst also taking down evildoers in society and saving the world when not in school.
Innovation/Expanding Could Make Persona 6 Even Longer
The thing is, with a game like Persona, any kind of narrative or mechanical innovations run the risk of being a double-edged sword. Obviously veterans of the franchise will want fresh takes on the Persona framework, like different ways to expand the social links/confidant quests with characters, or potentially different ways to make exploring dungeons/palaces more interesting. However, Persona still has to maintain that balance between JRPG and social simulator equally. If certain aspects of the game end up taking too long, or makes things too busy all the time, that gameplay/narrative balance could fall apart fast.
Weighing too far into either side of Persona's unique gameplay balance means players are going to start favoring one over another. The goal of a Persona game, at least from a player's perspective, is to generally have players place an equal amount of investment into both sides of the game's dynamic. Sure, there will always be players who suffer through the JRPG segments to get to the story or vice versa, but most players of Persona generally enjoy both aspects of the game. If ranking up social links takes too long before dungeon deadlines, or grinding character levels requires too much dungeon crawling over several days, then the game experience becomes woefully unbalanced.
Persona 6: Maintaining Proper Gameplay Balance
Of course, that could just be a vulnerability of the calendar system that Persona has been using since Persona 3. At the same time, that calendar and days-go-by mechanic is part of what makes adventuring through a Persona game interesting. The calendar helps contextualize in-game decisions in a subtle yet impactful way for players. Depending on how ambitious new mechanics become, and how they balance with gameplay time and in-game time, too much innovation could hurt the next Persona. Making dungeon crawling or the social simulator too busy has a great chance could be detrimental for the average player who just wants to enjoy the game.
That being said, the next Persona game will certainly try new things, especially with the series' director moving on to a new studio. Persona could significantly revamp for the next generation, which frankly could be yet another groundbreaking JRPG experience. So long as that gameplay dynamic between JRPG and social simulator aspects is well balanced, it shouldn't be a problem. There's just an inherent worry that any expanding of mechanics could turn a 100 hour JRPG into a 200 hour JRPG. No matter how big of a fan someone is, if a game's too long, player's attention spans will eventually dwindle and the game will never be completed.
Persona 6 is rumored to be in development.