Despite what the extended universe would have you believe, Palpatine is dead. His death was the catalyst action in bringing back Anakin Skywalker back from the Dark Side and into his son's good graces. It was the major act in a father's redemption story, and should stay that way. Palpatine had a specific purpose, and it was stretched almost to its breaking point in the prequels. We don't need to see where he came from (although it is pretty interesting if you're curious), just as we don't need to see all the backstories from the other characters in Game of Thrones that aren't pivotal to the plot. Need an example of how an origin story can neuter a once terrifying villain? Look at Hannibal Lector. The origin film, Hannibal Rising, took the monster out of the man, and turned him into something sympathetic. It's the inability to understand and empathize that makes a powerful villain, not the other way around.
