The 2nd Air Defense will be unlocked at Town Hall 6.
The 3rd Air Defense will be unlocked at Town Hall 7.
All these new sneak peeks have been revealed in the newest video from Galadon.
This is a pretty nice update for not only TH7 but also for TH6 since currently Clan Wars at TH7 are really boring with juts pure Dragon attacks. Also, Healer and Giants combo will be not OP anymore at TH6.
Take a look at here for the main page of this update.