I know you can change the directory from which JSON files load/save. However, this falls short when you’ve got themes and plugins that may need to establish editable field groups.
I’d love to see the ability to register JSON locations (directories). Then, when creating a field group, you could choose from those registered locations if they exist (otherwise the default location would be used). From that point on, that field group would save/sync from that specific directory.
What happens if the user changes the directory? Perhaps if the field value is changed upon saving the field group, any instances of the JSON file in other registered (or default) directories is destroyed – and a new one is generated in the new location.
I know there’s a plugin that attempts to add this feature, but this is the kind of functionality I would not be comfortable using unless it was a part of core ACF.