Schnepp, who recently directed The Death of Superman Lives: What Happened, a documentary about Nicolas Cage's failed Superman movie in the 1980's, is reporting that Miller will be directing Man of Steel 2 for Warner Bros., which will likely be released after Batman v Superman and Justice League. There is no confirmation, but according to Joblo, Schnepp seems very assured of this claim in his conversation with Popcorn Talk. Schnepp is the same guy who saw an early test screening of Mad Max: Fury Road and reported how incredible it was to everyone, so I definitely trust him. This also doesn't surprise me because of Miller's long-in-development Justice League film, entitled Mortal, which fell through back in 2007.
As much as I want a Mad Max sequel sooner rather than later, I definitely think that Miller could fit both into his schedule. Man of Steel 2 likely won't hit until 2020 or later, thanks to all of Cavill's commitments to Justice League, so Miller could film The Wasteland in the meantime and tackle the Superman sequel after that. But if taking on this film means sacrificing more Mad Max films, then I definitely don't want to see it happen. It's great to have a variety of directorial voices in the DC universe, but Miller created the Mad Max universe and I don't want to see it fade away because of other films.