As a heads up: If a rumor isn't coming from Sad Panda, Lady Atia, or the old staples of Hastings/Harry, then it's likely complete trash.
Sad Panda, who's been 100% right for over a year now, has said January will see new Fyre Slayers (AoS Dwarfs), and February will see a new Space Wolves codex (because... 'reasons!')
Lady Atia has also said that Wolves are coming early on in the new year.
The only thing that might be on the horizon for Chaos, is the new LoC, which Hastings has hinted at. (but no mention or even hints at another Daemonkin book)
GW is perfectly happy to let Chaos rot, as they clearly have no idea which direction to take the Chaos Marines in, while the model line is so far gone that it needs a Dark Eldar level overhaul. (and that's likely too much of a financial risk in the current climate...)
I'd be willing to bet that we'll see new releases for Wolves (confirmed), BA's, Tyranids and likely even Orks before anything major gets done for Chaos. (and at this point, Daemons are more likely than Marines, as GW can cash-in across both systems!)