This is just my theory... but from a marketing standpoint, releasing TOOC right after TA would not be good for T11 for a couple reasons. 1st, many of us have drained our accounts on TA and simply dont have funds for another big release like TOOC. 2nd, with all the material on TA, most of us wont need any more material to practice for quite some time; there's enough magic on TA to last a decade! So i'd assume T11 is holding off, perhaps refining TOOC, to make sure its top notch for when they do decide to release it.
Again this is just my theory, it'd be great if we could get an offical response. Either way, I cant wait for TOOC!