TL;DR
when going through a blueprint book instead of (or perhaps in addition to) holding shift to jump blueprints, holding alt should jump out of the current book it is in and go to the next blueprint in the overarching bookWhat ?
Let's imagine a scenario (this is a blueprint book tree)Blueprint Book #1
>Blueprint #1
>Blueprint Book #2
>>Blueprint #2
>>Blueprint #3
>Blueprint #4
normally when scrolling from BP1 to BP4 (without scrolling backward, just imagine there is a large book behind you) you would have to scroll through all 4 blueprints (I know that is not much but imagine a book with 100 BPs) now imagine if instead, you held alt when BP1 was selected, you should then skip over BPs 2 and 3 and go directly from BP1 to BP4
I would also imagine that if there is no Blueprint Book ahead of you (let's say you start on BP2) and hold alt and scroll you would instead jump out of your current Blueprint Book and move to BP4. In order to not cause headaches with BPB nested in BPB nested in BPB etc, this particular feature could only be used once per alt press so that you don't jump all the way out of your book