It now appears that the volumes are out, and ready to be ordered online! I can only imagine that the thousands of pages released in these books will spur a great amount of new interest in Stockhausen, as well as oblige many libraries around the world to redistribute their shelving in order to make space for some more linear feet!
As expected, the volumes cover the time from 1991 (where Texte 10 left off) to 2007, and contain the forewords for many scores as well as various concert introductions, lectures, letters and short interviews for magazines (according to Imke Misch's introduction in volume 11). The Texte include information not only pertaining to the LICHT-operas and KLANG cycle but also texts relating to earlier works, from KREUZSPIEL onwards.
From Misch's introduction in volume 11, we learn that a supplementary volume is also planned for sometime in the future.
I can only imagine that this must have taken an immense amount of work to put out, and so many thanks are due to the Kürten team!