Age is not a problem for Fujino. I mean, most anime parodies on this site are about teens.
Even in this one, the character models are much older than in the original series.
I'd like him to finish Sakura chapter first tbh.
As for a new game, honestly everything with magic works, it's Fujinos beloved tool to justify corruption.
I believe that Sabre is actually a challenging fmc from a writing perspective. Her original character is nearly emotionless, making it either very difficult to make her emotional developement believable or resulting in an extremely slow character development.
Persona 5, hmm interesting series indeed. Maybe it would probably work best as a sandbox NTR, where you need to actively try to prevent (or not) your chosen fmc from being stolen, but shouldn't be able to save them all. The good thing is, it works with every persona installment