Its a given that Necrons are the next 40k codex release. It can also be assumed that we will not see another codex release until the next campaign set starts up, which looks according to the latest rumors to be sometime around the end of April or beginning of May.
If you are keeping up on the comment section, you will know that Nightfury sometimes chimes in there with a little bit of information. This is what he was saying today about the time frame for the next campaign.
Please consider these rumors.
I think the big question will be, who will be in this upcoming campaign? Chaos Marines? Dark Angels? Maybe even the Adeptus Sororitas?
via Nightfury from the Faeit 212 Comment Section
The next campaign will start in late April or early May