Server Nerdacy emailed few days ago CD Projekt RED co-founder and CEO Marcin Iwinski to ask them few questions about the delay and hidden things behind the decision.
The answer was short and clear. The studio is removing the final bugs and optimize various areas. All of this is done to give players more engaging experience and the game should be better looking across all platforms. There is no changes being made in the content area. This part is already finished and all of us should get weeks of gameplay. It should be around 120 hours which is more than enough, don't you think?
There are also few notes about Ciri and the main reason why we will be able to play as Ciri is to allow gamers to see parts of the story not just from the perspective of Geralt.