Personally I strongly believe the game will be launched at march or april. For starters, they would not announce a game 500-pus days before release. People would end up losing interest not to mention the financers. We have all seen what happened to games like WAR when they were announced too soon.
Secondly, if they have been working on the game since either Shogun 2 or Rise of the Samurai, then I can't see why the developement would take up to three years to complete with a 40% larger budget and team. According to CA, the game is not that different to previous ones, as was the case with Empire. It even utilizes the same engine, although heavily modified. It won't "revolutionize" TW like Empire did with naval battles, gunpowder weapons, huge map, revamped adminstration, revolutions etc. Besides, it has already a Steam page, a trailer, a moderate amount of info and even a few screenshots, even though they are "pre-alpha". (which means nothing since Shogun 2 had also pre-alpha material six months before release.) That seems quite much for a game which is supposed to be released at december 2013, possibly even 2014 if you believe that nonsense. If you just wanted to announce a game, how much an effort do you seriously have to make?
Thirdly, this whole announcement thing seems strangely vague for me. It almost looks like they have deliberately told some companies that it will be launched late 2013, some that the release date will be summer/autumn, and then simply 2013. My two cents/pennies/sestertiuses would be that they have confused people as to the true release date to avoid a catastrophe like Empire. If they can publish it at spring, it will seem natural. If not, they can always state they stated a "late 2013" release. Most likely they are trying to play safe with this one.