I absolutely agree with you on the whole Arthur/Lancelot thing, Wynbish.
Peter Pan is a good guess, too, but like you said it doesn't really fit his Storybrooke persona much at all. I know many people have said that the Mysterious New York man is Rumple's son, but perhaps he's Peter Pan? It would seem a pretty terrible curse for a boy who doesn't want to go grow up to be stuck in a mundane nine to five New York job.
"Anybody that goes to the theater, I think we’re all misfits, so we ended up on stage or in the audience.” --- Patti LuPone.