Hello,
I found this site looking up this theme.
While I have no proof, I have nothing to gain in misleading anyone.
I email THG regulary about various themes and giving feedback and suggestions for them. I'm no insider, but about a week ago after another email to them, I recieved a call from one of the fine CSRs. During the conversation which lasted about 30 minutes, I was told outright that "I can see the yellowbrick road already." We also discussed the idea that Lego Dimensions should be supported by sets of locations and figures outside game. "Lord Vortech attack ing Oz, I love it."
While I understand how this information will be viewed, I strongly suggest anyone who wants to Oz sets should send the info to TLG and say so.