Diffusion should get a modern diffusion.search endpoint.
Diffusion should also get a modern diffusion.edit endpoint, but that is probably like 2,000x harder because of the huge multipage form and all the workflow logic it entails, so maybe I just punt that for now.
Our use case is that some repositories have special needs on the client side. We'd like to be able to create a special #project and tag it in Diffusion. For example, we have a custom arcanist workflow that takes special action before running 'arc land', but only on a specific set of repos. Similarly, we have use cases where CI needs to do some special checking depending on what is essentially a series of checkmarks per repo.
While some of this can be handled with Harbormaster and/or the new build work (T10329) going into arcanist, it remains generally useful to be able to see the metadata associated with a given repository.
This might be a special case of T5873 but I'm not sure