I got the info and picture from chibiyuuto's FB page:
Chibi Yuuto's CHRoNiCLEs The release date for Card Captor Sakura 20th anniversary edition ARTBOOK has been decided, it will be March 22nd, 2016
Said artbook, I remind you, will be Clamp's personal selection of their favorite artworks from the three previously released Cardcaptor Sakura Illustration Collection Artbooks, released between 1998 and 2001.
As of now, it is still not available for pre-order anywhere, and no further info about the content was revealed. Nonetheless, the release date being so close, I don't think we will be left wondering for too long :)