The books will be published with soft cover and size A5 (14,8 x 21 cm). The information came with a flyer that came with the 6th Kobato. volume (thank you ozaka_tomoe for letting me know about this!).
CLAMP CLASSIC COLLECTION
12/2011 - RG Veda #1
01/2012 - Tokyo BABYLON #1
02/2012 - RG Veda #2
03/2012 - 20 Mensho ni Onegai!!
04/2012 - Tokyo BABYLON #2
05/2012 - RG Veda #3
06/2012 - CLAMP Gakuen Tanteidan #1
07/2012 - Tokyo BABYLON #3
08/2012 - RG Veda #4
09/2012 - CLAMP Gakuen Tanteidan #2
10/2012 - Gakuen Tokkei Duklyon
11/2012 - RG Veda #5
It seems Kadokawa acquired Shinshokan's series and will republish them, along with their own early CLAMP works.
I think these new releases will not follow the original page count (they will probably have more pages), that would explain why there is only one release for 20 Mensho ni Onegai!! and Gakuen Tokkei Duklyon, and also why Tokyo BABYLON will have 3 books and RG Veda, 5.
With this, Kadokawa owns the rights of 14 out of 22 CLAMP titles (Kodansha has 6, Shueisha has 1 and Hakusensha has 1).