Hypermedia APIs

Everything as a Resource

Data model as a resource: Describing the data model as a resource could help build forms for entering data or interactive user interfaces. One vocabulary to assist here is the SHACL Shapes Constraint Language for describing graph data structures.
Hypermedia as a resource: The API itself can be described as a resource too. One way to do this is using Hydra, a vocabulary for describing APIs with RDF. This sort of self-documentation is similar to OpenAPI but could make the API discoverable at runtime.
Access control as a resource: The Basic Access Control ontology is another shared vocabulary for describing access control that was proposed by none other than Tim Berners-Lee.

Hypermedia APIs:

Will be trivially REST-ful, since they are simply what Roy Fielding was describing.
Should be driven by the needs of the underlying hypermedia application
May change dramatically without versioning information, because hypermedia utilizes self describing messages
Should be passed directly to humans, to maximize the flexibility of the system

Data APIs, on the other hand:

Will not benefit dramatically from REST-fulness, beyond perhaps Level 2 of the Richardson Maturity Model
Should strive for both regularity and expressiveness due to the arbitrary data needs of consumers
Should be versioned and should be very stable within a particular version of the API
Should be consumed by code, processed and then potentially presented to a human