Currently a chatGPT plug-in needs needs to implement a REST API server with an OpenAPI spec. Every graphql API automatically comes with formal, machine readable, documentation (via introspection queries). Considering that there is a rich ecosystem of tools which expose a graphql API ( for instance, hasura; disclosure: I work for them but speaking for myself), I think supporting graphql apis in addition to REST/OpenAPI’s could be really powerful.
(a similar question was asked here, but it’s not exactly clear what they mean: /t/graphql-support-for-chatgpt-plugins/181748)