There isn't a cross-grade path or discount for customers of existing libraries to the StaffPad Editions.
The StaffPad Editions sample libraries available within the StaffPad Store are totally bespoke, unique editions. These are created from scratch from the original source materials, licensed and created in partnership with 3rd party sample developers. They only work with StaffPad, and have been designed and rebuilt entirely for StaffPad's unique playback engine and concepts. They are very much their own products that are integrated directly in StaffPad and, as such, have their own pricing and StaffPad Edition branding compared to the Kontakt (or other sampler) based versions.