Persona VS lets players pick one of the protagonist characters from Persona 3, 4, or 5.
This might be overanalyzing thing, but Justine’s words might be hinting that this Velvet Stadium is where a Persona 5 actual fighting game will be taking place.
An actual Persona 5 fighting game can definitely happen.
Banso and Atlus announced on October 12 it plans to launch the “board game” Persona VS (Versus) in late December in Japan.