I have no idea on the tech side of things, but based off what Tabata has said, the game has entered the stage of development where all the story, gameplay design, set-piece, voice-work scripting are (most likely) all finalised, and they're basically focused on mass-producing assets without concern because there's no way the design of the levels/cities/dungeons will change at this point.
Chances are that the engine from an asset standpoint is pretty much complete. And the finalisation of the engine from now till spring are probably more on the mechanics side of things. And game mechanics will probably be finished long before they finish building the final dungeon of the game.
(Disclaimer : unfounded guesswork, etc)