> You probably would need to adopt a rule of no direct-to-table access, and a separate schema per API version containing views, and dealing with the pain of rewriting the views for all the supported API versions when you need to change your data model.

My understanding is there is no direct-to-table access with PostgREST; you're only ever interacting with views. Keep your view api versions in separate schemas. If you change your tables, yes, you'll need to update your views, but I don't see how that's much different than having to modify ORM code to accommodate schema changes.