There's a little while yet. The material itself is still being written and playtested as we speak. Since it's another core system, we want to make sure it's as solid as possible.
That said, one of the nice things about PDFs is that they don't have quite the same extensive lead-in time that print books have.
We'll keep you folks up-to-date on all that.
Developer, Song of Ice & Fire
Green Ronin Publishing
"A reader lives a thousand lives before he dies. The man who never reads lives only one." - Jojen Reed, A Dance with Dragons