This is tougher than some may initially suspect.
The potential of this is higher than any of the other rumored biopics out there, ala THE BEATLES. This certainly has the potential for spectacle and flair of ELVIS though it isn't any creative hands ala Baz Lurman. MJ was/is insanely popular for decades, unlike Whitney Houston (no offense) who an extremely high but much shorter peak.
The issue is...like Whitney, MJ was more or less a joke act the end of his life. Also like Whitney, pretty much everyone over the age of 30 remembers it. The guy hanging his baby off the balcony, SCARY MOVIE 3 spoofing him as the ghost - IN THE TRAILERS AND TV SPOTS! Obviously the pedophile stuff. And then of course, prescription drugs and eventually death. There is no triumphant, happy ending.
Unlike Elvis or Freddie Mercury, whose tragic stories ended decades ago allowing enough time to pass for people to rediscover them, MJ's problems and death still feel recent. I am not so certain there is a huge hunger for the over 30 crowd to go relive all their fallen idols problems at the end of his life.