UPDATE:
I tried adding LOADS more capabilities and still no luck. How can I make this plugin work for editors.
I tried adding LOADS more capabilities
…LOADS, even when written in all upper caps, is no proper description of what you have tried as it’s impossible to reproduce your steps.
There is exactly one capability check (see source) in the is_allowed() method that only runs during the AJAX request. It checks for edit_theme_options.
You will have to take a look at core to see why your authors can’t do that. I assume the problem will arise with pretty much every plugin that adds content at the nav menu.
Turns out that this did work. It was just hidden from the screen options menu for some reason! Thanks for the help 🙂