Pillar Chase 2 devs dislike FPE, meaning that chances of FPE characters inclusing Fen being in the game is low, plus we already have a skin for Baldi that references Miss Circle, PC 2 devs used Springtrap, Baldi and now gone Ao Oni and Fuwatti without creators permission, Camp Cataclysm devs on the other hand have permission to use all the characters that are currently in the game, the reason why they did that is because they don't want to get copyrighted, Herobrine technically can be added since he doesn't have an owner, meaning that he's technically public domain.

FPE and Fen should technically also be on the same spot as Herobrine, since creator of FPE left the internet and even if she returns, she won't be making content about her old projects, meaning that she doesn't care that people are using her characters in things like video games, so that means that Fen can be added to the game, but it depends on what Camp Cataclysm devs think of her, they deconfirmed TMITS because they don't like him, so all FPE fans can do is pray to God that Camp Cataclysm devs don't dislike FPE or Fen.

In my opinion it would be cool to see Fen as a playable monster, or atleast as a skin for another monster of devs choice.