GenCon 2014 is the likely date. The *might* be able to get a small book out for June or July, but that would be pushing it. So they'll have wasted 2/3rds of their 40th anniversary with nothing in stores. Really, it doesn't even look like they have a single product out after December (although we know one other adventure is coming...)
Another thought that crossed my mind is that they could come out with a beta product, one that is semi-finished, that would allow them to kill two birds with one stone: Increase excitement about the game and get another round of feedback to make sure they've got it right.
Pretty much set for 2014 unless something disastrous happens. As Canuck pointed out - the 40th anniversary is next year. Its mind share during the next year among ex-gamers and non gamers should be higher than it has been at any point in the last decade. And that'll be just from free advertising from the 40th anniversary stories. Add a large, paid, and aggressive advertising campaign for Next into the mix, and you should see the new edition do very, very, well.
Unless Wizards marketing team is completely incompetent that is.
I'm pretty sure that WotC is going to drop a bomb and start releasing the game on January 2014, probably a basic box set with basic D&D with rules for levels 1-10. Several months later they will release the core books of the standard version.
Warder
I think you are over-estimating the amount of playtesting that WOTC will do. They haven't exactly been known for their editing and playtesting up until now.Is there anyone here who can comment on the logistics of publishing? It seems to me that the act of publishing will take several months, what with proofs being printed, proofread, errors in the text and formatting and artwork etc caught and corrected (there'll probably be at least two rounds of that), and so on. And then stock must be printed and shipped to your FLGS ready for the release day. And there will always be delays. And before that there must be extensive playtesting (and therefore fine-tuning) of the final product. So, for a release at GenCon, August 2014 we're looking at the game being print-worthy sometime in April at the latest, with final in-house testing probably taking a month or two, bringing us to February, which, with Christmas, is nice time for a final closed playtest packet.