Evangelion, Gatchaman/Battle of the Planets, Macross/Robotech, Patlabor, Battle Angel Alita (I heard James Cameron was interested in filming an Alita movie), Gaiking... All of these manga/animes have something in common: they have been in development hell for years and years. Honestly I see no one of them happening.
And when it happens... Results may not be pretty. It has been made movies from Fist of North Star, City Hunter (Jackie Chun cast like Ryo Saeba... I do not get why), Casshern, Devilman, Cutey Honey, Kekko Kamen (Kekko Kamen, for God's sake!)... And most of them have been awful. Fist of North Star fans don't let their friends watch the Fist of North Star movie. You have been warned.
Did you know many years ago a DB movie was done? It was done in Korea or China, I am not sure... Regardless, I saw the tape in a videoclub a day -back in the nineties-, but I did not rent it. I heard it is so awful it is hilarious, at least.
I do not say a good movie can not be done. Space Battleship Yamato's movie was pretty decent, or so I heard. But it is hard, and the odds are against it. Several producers have approached to Go Nagai to buy the rights for a live-action Mazinger-Z movie, but he has not taken up any offer so far because he needs being sure of it will be a good movie.
Hmm... Honestly, I think that a anime/manga movie needs being easily adaptable and having mass-appeal to succeed. That, and having a competent producer, director, cast... of course.