Just curious about the bolded there. I'm someone with way, WAY too much knowledge about the history of the Oz series, and from what I know neither Disney nor Warner Bros. actually own any of the concepts from the sixty or so books that make up the original series, the first half of which are all in the public domain.
Sure, you do have things like the Ruby Slippers and characters like Miss Gulch or the Lollipop Guild, which are not from the books and which Warner Brothers owns the likenesses to, but none of the main characters from Return to Oz are owned by Disney. Jack Pumpkinhead, Tik-Tok, Mombi, Billina, the Wheelers, the Gump, the Nome King, and Princess Ozma are all public domain characters.
Overall Oz is such a tough IP to make work in my opinion. Sure, the source material is overflowing with rich characters, locations, and concepts that would likely translate really well into a modern kids' action adventure franchise, but so much of what actually gets developed is adult "Dark fantasy" re-imaginings of the MGM musical... and they are almost always awful by comparison.