I think the jury is in: GraphQL is a winner for developers consuming APIs. We format a request for the exact data we want, and the endpoint coughs it up. What might have been multiple API requests and manually stitching together data, is now one in just the format we want.
I've heard less about whether GraphQL is ideal for the providers of those APIs. I imagine it's far easier to cache the results at specific URL's with a REST structure, as opposed to a single URL in charge of any request. But I'm no server guru.
This tool is pretty fascinating in that is allows you to build your own little GraphQL backend and then run queries against it and see the results.