I've only played with these kinds of plug and play databases, but mixing and matching seems like the worst of both worlds. The plug and play is gone, because some things might me in API 1, some others in API 2, and maybe worst of all, their domains might overlap. So you need to know that the "boring" changes happen via the postgREST, but the fancier ones via some custom API. The APIs will probably also drift apart in small ways, making everything even more error prone.