"So what's it about, then? "
Not working at GW I don't actually know, of course. However the Slaanesh in hiding thing makes sense given how things wound down in the Old World. Also it gives them a good opportunity to keep the elves out of the game for a time while they are figuring out how they want to re-imagine the elven models. So this set of releases is mostly Khorne vs. Sigmarites. They have also done some stuff with Nurgle and Treemen types.
Tzeentch has been in the books but obviously not a focus, nor has Tzeentch had any new big models come out like the Slaughterbrutes or whatever they are and the Blightkings.
We might see Tzeentch and dwarfs or something and then Slaanesh and Elves.
But who knows. It certainly would be a neat narrative thing and a way to keep interest up.
Of the Chaos gods the two that make the most sense to remove for a time are Nurgle and Slaanesh. You could probably come up with ways to temporarily take out Khorne or Tzeentch but it would be harder to fit in with the narrative.
Of Nurgle and Slaanesh Nurgle has a bunch of pretty new models, Glottkin, the Maggoth lords, the Blightkings and the plague drones, plus possibly others, I've only just started doing Nurgle.
So you can't get rid of Nurgle, but you can get rid of Slaanesh and if you have problems in deciding how you are going to do your Elves Slaanesh has a much better connection with them than Nurgle does.