Currently, Adobe does not allow to use their products on servers. So, for instance, you can't have a website app with mock-up generator with Photoshop on server-side hidden in the background. They do have Photoshop API for servers but it is a different product with yet unknown business model and it is in the cloud and not "on-premise" https://www.adobe.io/apis/creativecloud/photo-imaging-api.html
I know that you are working on Plugins for Affinity so I have 2 questions:
Will you allow server usage?
Will you have headless mode? No dialogs, no windows, no need to render canvas?
If you feel that server licenses should cost more... that is fine if price will be reasonable and predictable. Otherwise, people have to use ImageMagick which is free and quite feature-rich tool.