Here's a weird news story: the Edgar Rice Burroughs Estate has announced that Disney has lost all the TV/movie/merch rights to the John Carter books and that they're looking for new partners to make new John Carter movies. That's weird because A Princess of Mars, the first John Carter novel and the one that introduces a lot of the characters and concepts of Burrough's Barsoom, is in the public domain. I think a few of the other books are in the public domain as well.
This is where it gets tricky, and where my legal knowledge falters: the stories are in public domain only in the US, which means that international releases of any non-licensed John Carter movie could be impossible, and international gross is everything. And it gets trickier because the ERB Estate TRADEMARKED a whole bunch of Barsoom-related titles and names, which I believe is technically not allowed under US copyright law (you can't trademark shit in the public domain, and Johnny Carter and Dejah Thoris and friends are public domain). This is how they went after Dynamite Comics, who were publishing comics based on the John Carter characters.
All of this is kind of pointless, though, as nobody's going to make another fucking John Carter movie anytime soon. By the time somebody wants to take another big swing at it, all of the ERB Estate rights will be long gone - unless corporations keep monkeying around with copyright, but that couldn't happen, right?
I liked John Carter of Mars, but I just don't think there's a viable movie franchise to be found there. The ERB Estate is working with Warner Bros on a new Tarzan movie, which makes more sense to me, but Barsoom is probably uninhabitable.