There has been a little talk of late about the soft cover codices getting replaced and updated in a very quick manner. In fact, we have heard this a couple times now, but just how quick these replacements will be is rather speculation right now.
Please remember that this is a rumor, and please consider it vague right now. We have very little to go on right now, saying that Necrons will come next. The only thing we have, is that the codex vanished on the site. I am really hoping that we will not be seeing short 1 week codex releases.
via Larry Vela on Bols
New talk is doing the rounds on the Necrons coming in the months ahead, on the heels of Grey Knights.
Codexwise: the Necron codex is described as being a minimal updated codex, similar to Grey Knights, crammed into a very short release window.
Models: Unlike Grey Knights there is talk of a new combo-plastic kit for Destroyers which will include the parts for Heavy Destroyers and Necron Destroyer Lords. There is mixed chatter on whether the clear green rod will be replaced with standard plastic.
Timing: Look for these to be coming in Fall.