Since there are tools for OpenAPI to generate clients and test API calls, it'd be nice to have the rest-api documentation available in that format.
On a somewhat related note, I imagine you'll want SDKs for different programming languages (PHP, python, ruby, c#, etc.), perhaps an OpenAPI spec would make it easier for 3rd-party developers.
dexie-cloud looks very exiting, congrats and good luck on the release!