Author here. There is a part 2 to this: https://stoppels.ch/2022/11/30/io-is-no-longer-the-bottlenec...
Some other participants said that they measured 0 difference in runtime between pshufb+eq and eqx3+orx2, but i think your problem has more classes of whitespace, and for the histogram problem, considerations about how to hash all the words in a chunk of the input dominate considerations about how to obtain the bitmasks of word-start or word-end positions.