Is it going to be directly related to the film ?
Or go off at more of a different angle, and have Sleeping Beauty the Disney Classic as a distant related cousin ?
I would imagine that they'll have to take a few liberties with the story of the film in order to make this new interpretation work. If you look at "Wicked", a similar "story-behind-a-villain" adaptation, you'll notice that the Elphaba presented in the musical is nothing like the evil, cackling, one-dimensional villain in the film, even in the scenes in which the musical and movie cross-over.
The villain played by Margaret Hamilton and the character portrayed on stage all over the world are just too different, and even if we are to believe that she had a motivation for the bad things she did, the villain we see in the film just couldn't line up with the character that the musical wants us to believe she is.
It's an issue I think always occurs with these "villain's-backstory" re-imaginings. I read a Disney-published novel by an author who I think is called Sophie Valentino (although I may be mistaken, I can't remember), the novel was named "Fairest of All: A tale of a Wicked Queen" and told the story of the Queen from Disney's "Snow White and the Seven Dwarves". The novel, while alluding to and featuring many of the events from the film, just didn't line up with the material it took inspiration from.
I'm not saying it's entirely a bad thing, but it's sometimes necessary to veer away somewhat from the source material when trying to tell the same story from a different point of view.