They are still a long way off, at least a year away from what I have been told.
of course now I have said that I will probably be proved wrong, but I am 99% sure they won't be this year.
Tau on the other hand are a strong contender, although they have had models ready to go for over a year and still haven't shown up.
2012 looks like this as far as I know:
February: Nids Wave
March: Necron Wave
June: Chaos Legions
July: 6th Edition boxed ste (featuring Dark Angels and Chaos)
August: Codex Dark Angels
There are no signs of any other Codex releases, there may be waves for other armies.
Q4 this year will be dominated by the Hobbit so expect Q2 and Q3 to be 40K centric, but don't expect too much.
Then Q1 2013 will be more Hobbit, Q2 2013 may see a new Codex but it's more likely to be wave releases, so if Eldar or Tau were coming I would say Q3.
Of course I may be wrong, but these are the indications I have been told.
Then again, one of those sources said Tau were due before Necrons, so who knows....