I either have my dates mixed up or the next TCG deck release date has been pushed back. In any case, according to WoWTCGLoot Betrayal of the Guardian will be out shortly before the targeted week of patch 5.2 release. Appropriate since the patch is necessary to put the Gusting Grimoire in the game. :P
WoWTCGLoot has also updated their pre-sale announcement with the pet that one lucky pre-sale purchaser will win. It's Grunty! There are also other prizes for the new loot as well. You can review them all here.
If I remember correctly, the Gusting Grimoire shares similar abilities to the Lofty Libram, with a couple placement differences and alternate attacks. I have yet to try using the Lofty Libram in a battle, so I don't really have an impression of how books battle. ;P
Anyway, the pre-sale for the Gusting Grimoire is still going on, so don't miss your chance to get the grimoire as it's released and enter in to possibly win Grunty. :D