I think it would be pretty nice if you could press Space bar and scroll down the note like you can scroll a webpage in Safari. Shift+Space would scroll note upwards. This would obviously work only when a note is selected in the note list but editor isn’t activated, as currently pressing Space does nothing when in this state.
In an editor the spacebar has a fundamental meaning: to add space to the text 
Making it dependent of the editors state and other stuff would lead to confusion of many users. Maybe another key?
Space bar has no function in note list state so might as well; that’s my reasoning for it. But I would be totally fine with any other shortcut too.
Edit: and good point.
It has when you are typing something in the search field
Page Up + Page Down?
I use the two finger gesture on trackpad for that. I love trackpads or mice
Page Up + Page Down?
These scroll the note list up and down currently. But it could be anything really.
I believe if the focus is in note rather than notes list though, it will scroll that instead