Vol 4B was partially published in fascicles: https://www.amazon.com/Art-Computer-Programming-Fascicle-Pre... and https://www.amazon.com/Art-Computer-Programming-Fascicle-Sat...
Instead of the ultimate edition of vols 1-3, so far we've got a "patch" by Martin Ruckert who coordinated the volunteers: https://www.amazon.com/MMIX-Supplement-Computer-Programming-...
[0] https://www.amazon.com/MMIX-Supplement-Computer-Programming-...