Hi!
Here is one change that would make my life a lot easier:
Use case: when reading a book, I would like to be able open any note file and edit it on the side-by-side view.
I have note files per topic, so when I am reading something, I would like to be able to open a note file on the side-by-side view and add or edits my notes in there, and switch between the files.
I also use the per-book note files, to do some math mostly, and probably never looking at those notes again (so I use it mostly as I one time thing, but not always) . 
Don’t know but maybe more people have a similar use case.
Regards,
Eberli