Well, to be fair, there are two categories for future games related to PS
Spin offs and Extra Content.
The spin offs will be free and will not be as complex as Predator's Syndrome and the Extra content, and will have stories about characters that don't appear or aren't a main focus in the game.
The Extra content, it's going to have stories related to the Love Interests. Such as how their lives are with the MC after the Good Ending and (Currently being developed) an NSFW Expansion that, like the name suggests, will have adult content of the main 5
Only the Extra Content won't be free. I don't know how much they will be, but, at least the NSFW Expansion will be above 10 USD because of how complex it is.
I hope I was able to clear up your doubts!