It is an entertaining article, but I am not too sure if I agree that Knuth was yak shaving. However by luck, inspiration, conviction or observation he understood what makes a program last. You focus on one thing and you do it well. On the way you resolve all the problems. He famously said that at first he had one user: himself but then things were different when he had 1000 users. At that stage you need to remove bugs and hence his famous checks rewarding people that reported bugs. When your user base grows allow them to extend the program through their own code. I also think that the program adapted well, throughout the four decades of its usage due to the well thought level of abstraction. Nearing my three score and ten years, and using TeX/LaTeX for all these decades, I can with confidence state, that the only people yak shaving was us all the early adopters, learning typography rather than focusing on our studies. The same can of course be said for current users.