This seems like such a basic feature to want and by definition it will be the evernote power users (i.e. their paying clients) who want it. PLEASE PLEASE PLEASE implement this instead of vanity projects like Dark Mode.
Edit: Just noticed my Subscription:BASIC badge... do you know why? Because I have developed master and slave accounts with certain notebooks shared between my accounts as part of the workaround to this missing feature.
Evernote is a productivity tool, therefore help us remove information bloat and contextually irrelevant interruptions by helping us build a system that works for people in their various life roles and focuses. Come on guys!!