I too am a fan of Edgar rice Burroughs great adventure novels. I may be in the minority by preferring the Carson and Pellucidar series to Mars, but they are all great stuff.
Last official news I heard, the guy (cant remember his name??)who was responsible for Sky Captain was helming the film, and presumably using the technology he created to make Sky Captain to bring ERB's world of Mars to life. Unfortunately, because Disney is involved, the licensing is pretty much predetermined and already locked in before the first roll of film is in the can!!
"Crayons taste like purple!"