Turns instead of years may be a very useful concept. It solves -or seems to solve - several design issues such as the movement time across land and see, sieges, the opportunity to include seasonal changes without having too much turns in a campaign and it may even add to immersion. Though it may very well become a broken feature adding nothing but absurdity to the game.
We will see when the game comes out whether this was a good turn (no pun intended) or a bad one. But my fear is that programmers may be blinded by the opportunity and not see its dangers. Only a beta-test can reveal whether this is well received by the average player. If that is the case, will it be possible to turn back (again no pun intended) to the old system?