Would his "next volume" be #4B, or #5?
Notice the length of time between first release of #3 ("Sorting and
Searching") and PART of #4. Only slightly longer than it takes me to READ
it! (His works have the highest information density of anything that I've
ever read)
It would be wonderful if he were to live long enough to finish the series!
His plan for the last several years has been to finish 4A, 4B, 4C, and 5,
then to do new editions of 1-3 using MMIX and adding new material
that has come along since the last editions. Then he plans to do a
condensed edition of 1-5. Finally, if he lives that long and there's
something to say, he'll work on 6 and 7.
The time between 3 and 4A was certainly long, even figuring on 10
years or so for TeX. But even though no new TAOCP material appeared
until about 7 years ago, he was writing other stuff. Given that he's
got enough of the Ch 7 material together that he's got one volume
through the publication process, there's a good chance the tme between
4A. 4B, and 4C will be more like the time between the first editions
of 1, 2, and 3 than that between 3 and 4A.
BLS