While the registrations for Persona 8-10 are almost certainly a forward-thinking move by Atlus to secure the names for the distant future, the P5-related domains could point to new spinoff games. After all, Persona 4 received several spinoffs, including the rhythm-based Dancing All Night, which, oddly enough, has a Persona 5-inspired outfit hidden in its game data. Persona 4's other spinoffs include a pair of fighting games, Arena and Arena Ultimax. As such, it's quite possible that P5D.jp and P5U.jp are for Persona 5: Dancing All Night and Persona 5 Arena Ultimax, respectively.
It's also worth noting that a crossover RPG called Persona Q: Shadow of the Labyrinth, which features the casts of Persona 3 and Persona 4, released for 3DS in 2015. The registration of PQ2.jp could suggest that a sequel is on the way.IGN has reached out to Atlus for comment and will update this story when we receive a response.
For more on Atlus' stylish new role-playing game, read IGN's Persona 5 review to find out why its "gorgeous, vibrant world and captivating story make Persona 5 a new gold standard for Japanese RPGs." While you're at it, check out this overview of all the new outfits and music coming to Persona 5 as DLC. Alex Osborn is a freelance writer for IGN. You can follow him on Twitter and subscribe to his YouTube channel.