Allow admin to configure the elements in the admin bar, user role based. Add new items eg. I would love to put 'plugins' into the +New dropdown, nest submenus into the admin dropdown menu, non-standard things like that.
I don’t think this is something that needs to be included in the core, should stick to a plugin like https://wordpress.org/plugins/adminimize/
Definitely a plugin should handle this. No need to bloat core with functionality that will not be used 100% by all users.
I think a lot of people would use this functionality, but agree that it's plugin territory.
+1 this should be a plugin, unless we totally redesign the old, outdated admin menu system.