In an earnings report, CD Projekt elaborated on its reasons for delaying The Witcher 3: Wild Hunt into next year. As translated by NeoGAF user boskee, the presentation once again describes the company's desire to better polish the game, as well as there being less competition, more Xbox One and PlayStation 4 owners, and the potential for a more effective marketing campaign given the new February release date. You don't say!
In terms of remaining work on The Witcher 3, CD Projekt RED is still finishing up side quests, locking in voice overs, testing and balancing gameplay, optimizing its REDengine 3, and, up until the bitter end, improving the quality of in-game assets.
The report also mentions a new mobile game that hasn't yet been announced at the time of writing. This is coming in addition to The Witcher Adventure Game and is being worked on alongside an external studio for release this year across phones and tablets.