I’m going to stubbornly stick to my guess that whoever else he may be, August is the librarian, the caretaker of the book, the gatekeeper to knowledge. And I think he’s OUAT’s Desmond, that is, he has some unique ability that will enable the hero, Emma, to access FTL, as Desmond did for Jack.
But if it turns out he’s not the librarian, I hope that someone is so that Storybrooke Library can go back in business.