Apparently this has been picked up by Warner Bros, and I really hope they move on it soon...
The only difficulty I can see with filming it is the time slip, in that it is a coming-of-age story, and they'd probably need two castings for many of the characters.
I certainly picture certain actors in the roles, but if I really think about it, I'm picturing them at their peak, and many of the actors I had in my mind's eye (like Sean Penn for Larry, Theo's dad) are probably too old now.
I definitely see Cate Blanchett as Mrs Barbour, and Rachel Weiss as Theo's mother, Audrey. Bill Nighy or even Liam Neeson could play Hobie. Boris is a plum part, and I think Ezra Miller or Adam Driver would be great in the adult role. I see Cameron Diaz stealing the show as Xandra. Would Christian Bale work as Larry, the one-time actor turned hasbeen gambler?
I find Theo the hardest to cast; there are plenty of actors I visualise, but most of them are distinctly past it now in terms of age. Maybe an unknown is required?
Anyway, I'd love to hear your thoughts, silly though the whole question is, but hey, if we can speculate on royal baby names, then why not this?