I really don't like the idea of it coming out in december. for the simple reason that since the steam winter sale will be going on and that might (and probably will) affect the sales greatly... if the game is released during the sales I doubt that many people will buy a 40 euro game instead of 5 games for that price at 80% off or something.
That was a remark from someone else on the Fan day too. Not because of the Steam sales itself, but because December is busy month for gaming in general: all major publishers want their triple AAA title out before Christmas plus we are also getting new consoles this holiday season.
But they (Larian) doesn't really care about that: DOS is a hard-core RPG PC-game, thus it's only for a niche market anyway. This won't be a blockbuster title regardless in what timeframe it comes out. So the release will be as soon as it's done and it won't be pushed backwards to 2014 because of marketing issues.