Sh*t I can't stop smiling this is adorable.
Hayasaka will always be welcome. This AU is a bit weird, but who cares? We got Haysaka-sensei, Shirogane-sensei, and Kaguya-chan.
The best part of Kaguya-sama is that every character has a more or less genuine relationship with everyone else. I haven't seen any doujinshi that take advantage of this, but I feel like there are ways to write just about any ship convincingly, sweetly, and with chemistry.