Originally Posted by
Varodoc
The Jailer is an ancient evil who seeks to consume the entire cosmos, as mentioned several times by Blizzard. Sylvanas, in her twisted mind, believes she's doing a favour to all mortals, but the Jailer is entirely self-serving. That's why I believe Jailer will eventually betray Sylvanas, he just wants to consume everything. He probably told Sylvanas that he'd set everyone free in order to bring her to his side, but he sees her as another disposable tool, and he certainly doesn't feel altruistic towards mortals.
However I don't think Sylvanas will redeem herself in any way, she's wronged too many people to be forgiven, and I think Blizzard learned from the Grommash fiasco. However, I do think Sylvanas might feel some remorse once the Jailer backstabs her, but nothing more.
The Jailer, and not Sylvanas, is the main villain and central driving force of Shadowlands. Never forget that.