Update via Eurogamer:

CD Projekt has revealed how The Witcher 3's upcoming new game plus mode works.

Posting on the CD Projekt Red forum, community chief Marcin Momot said enemies will be stronger when you play the game again through new game plus.

Player experience, items and alchemy recipes all carry over. Of note: if you're below level 30 when finishing the vanilla game, you will be bumped to level 30 for the start of NG+.

You also get a free Clearing Potion at the start so you can reset your skills and try a different build.

Also of note: items that carry over exclude quest items, books and letters, Gwent cards, usable items and trophies.

When you start a new game plus you can select any difficulty level, and you can obtain the Death Match achievement while playing NG+.