Daemons don't need an update, they need to be discontinued so that Chaos can get their daemons back.
You know what, I used to agree with this. Not sure any more though. Daemons have some real character on their own but their current codex seems like a quick fix type book. It's not awful and it had potential but it seems they just wanted to get it out there and didn't go as far with it as they could have. Toss in a few more unique Daemon Engines and some better thought out deployment rules and more choice of Daemonic Gifts and it could be fantastic.
Now having said that I do want Daemons back in the Chaos Marines codex but I'd be more than happy with just the lesser daemons to add some daemonic flare but just enough to not steal the Daemons' thunder.