For once, it looks like they’re introducing a character that is legitimately connected to one of ONCE’s protagonists in the world of fiction in a way that’s not egregiously shoehorned or just straight up cynical Big Mouse opportunism.
At the same time, I’m nervous. I grew up with Stevenson’s books, and adored them. I’d hate to see OUAT butcher these stories and characters. Also, how all of this factors into the Underworld plot, I’m not sure. Except that the concept of the “black spot,” or “black mark” which the POC Dead Man’s Chest “borrowed” originally comes from Stevenson’s Treasure Island. So that’s another connection, however tenuous.