Is there actually an SDK or API that allows 3rd party developers to build interfaces?
Or a library that can be used to create thumbnails and previews from the proprietary Affinity Photo and Designer formats? Not even ImageMagick which can handle almost any file does this trick by now.
Supporting ImageMagick by helping them to understand your file formats would be a superb door opener for your products to reach commercial customers. Alternatively you might give developers a library that allow creating thumbnails and previews, maybe with a command line interface.
All the big publishing companies, photo and ad agencies with their huge numbers of users are waiting for an alternative to their costly Adobe products, but they often need to integrate with other systems. So far, they watch what you are doing but they would not switch because they could not do the integration.