I don’t want to sound argumentative as I consider this a learning opportunity, and you force me to double check things 
Not sure if you have read fast after 50 lately, I just did a quick skim to make sure I was not missing something but if you remember most of the book focuses on high intensity training, and after many chapters of discussing this he has a section titled “Guidelines for high intensity training” and his first mention there is 3 minute intervals, 1 minute rest.
And here is another title and section with suggested workouts from the book.
Suggested Training Details for High-, Moderate-, and Low-Dose Workouts
I am not saying he does not suggest all out efforts in the book. I am just saying this is not the primary focus of his suggestions.
Also if you want to increase mitochondria in minimal time look at Blood flow restriction (BFR) that will give you fast results and at lower intensities. I have a BFR device, just for testing…
But none of this is actually my point. The point is TrainerDay is super small and don’t even have time to get stuff done that lots of people ask for, so trying to do stuff that so far only one person has asked for is not something that we can afford. I was just explaining partially why I believe super short intervals are not popular. If and when they are, I am sure more people will discuss or complain about this issue of >200% intervals. I would like to improve your experience with this.