via an anonymous source from the Faeit 212 inbox (very reliable source)
As I told you about a year ago, there are going to be more supplements for pretty much all the codexes, even Chaos Space Marines and Tau: though no work has really been done on the latter.
There is not going to be another Eldar one in 2013.
White Scars is one of the supplement codexes, and it is also complete (borderline printed) so logic dictates it'll be released a few weeks after the SM codex, but I don't have a street date for you.
Space marines will be getting 2 supplement codexes though by the end of 2013, so again... chances are white scars will be one of them.
For the Blood Angels and Space Wolves players, fear not you will be getting full codex support and not just supplements. Read between those lines.