Hugh, for a number of reasons it makes more sense that we build the GraphQL API for re3data, mainly that we run the infrastructure already anyway, and that we committed to build the API in the FREYA and FAIRsFAIR projects.
I have now built and launched a first iteration of the re3data GraphQL API, accessible via https://api.datacite.org/graphql. It provides the query parameters from https://repositoryfinder.datacite.org, in particular those relevant for repository recommendations (filter by subject area, data is openly available, use of PIDs, certification). An example query would be
This returns the fields specified for all data repositories in the humanities (subject area 11 from the DFG classification used by re3data) that are open, use PIDs and are certified. Including the datasets from these repositories (if they use DataCite DOIs) is one of the next steps.
There are a lot of things you can do with this GraphQL API, from exploration using Jupyter notebooks to services that use re3data data. I hope that makes it clearer what I had in mind. Also happy to have a call for a chat, if that makes things easier.