I have a similar workflow for adding content to my wiki (https://github.com/davidgasquez/handbook) from the computer.

On the go I'll add a task to taskwarrior and get reminded when I sync it from the PC.

>What would be even more amazing is when you can take ability to note under any line in a book (as Holloway already lets you), and see everyone's notes for any line/chapter of the book/paper you are reading.

I haven't used it but sounds similar to what https://web.hypothes.is/ is trying to do.