I mean, IMO it's really simple for people to just put "NPC" on their character sheet.
...But it's fine by me if people really want an NPC thread?
On the GM side, I absolutely do not want to spend my time maintaining NPCs. There's simply too many of them and it's not a very good use of my time.
IMO, there's not really a strong reason why the references rule in the Library makes sense with NPCs.
Most NPC's are the brainchild of a single individual, so they usually have a set appearance, personality, backstory, etc at the time of creation. It's not usually expected that NPC's will grow or change dynamically like a "Slime" Library entry might.