I just completed watching LOST, so there were many actors there that would be great in small roles just like Dale (Spencer) or Garcia (Tiny). Not to overwhelm OUAT with them but they really did have a great (and very large) cast.
Why not a Scottish trifecta with Henry Ian Cusick (Desmond)–he can play Rumpels father since they scrapped the earlier flashback stuff.
or for Hook’s father or pirate mentor (Blackbeard?), Mr. Needs-no-Guyliner himself, Nestor Carbonell (Richard).
Or Katie Segal (Helen) as Ursula or a cyclops (she does the voice for Leela on Futurama). And Dominick Monhagan would work as an aged up Peter Pan–especially an angry one (Charlie….but very recognizable as a Hobbit from the LOTRO movie.
I think though they may feel they’ve tapped that well too often, so might prefer avoiding anyone very recognizably from that show.
For the recast on RH, I wouldn’t mind if we see the character again much older, but I can’t think of an actor right now for that.
“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass