Do you think the disney villains should have a movie on their backstory?

Maleficent does, and they're already making a movie for her. Other than that, no.

I think it could very interesting to see how they have developed such hate and rage. Similar to how we learned why Randall hated Sully in, "Monster's University". I don't have high hopes for "Maleficent" because of the live action sequel to Alice in Wonderland.