Absolutely loving this addon and have been using it a lot for personal projects and shortfilms. It's a fantastic way to workaround a big limitation of Blender's Linking system.
But I honestly think it's super powerful outside of that as well. It allows you to create shapekeys "after" modifiers relying on Rest Position like Corrective Smooth and more. Which is why I'm wondering if this addon could be enabled for non linked and overridden objects as well. Since I personally see a lot of usage regarding this addon outside the overriding workflow too.
Heya, glad to hear you found use for it! Yeah, letting it work on non-linked objects should be just a matter of not restricting the UI, I wrote a note down in case I ever update this add-on.
This tool has been a huge help for a lot of my previous characters and I hope it'll continue to improve! I wonder if the upcoming Storm and Facial Rigging Project will reignite this Extension a bit.
So glad to see this addon on the extensions platform, it's become a must for me!