Huh, I've been thinking about a very similar service that does not require a dependency on GraphQL — https://poll2hook.com/ You can define a query on any API, be it GraphQL or REST, and a jq query to extract events, and you are good to go. I wonder if this @live directive is implemented with polling?
You could also implement live queries using polling and the E-Tag, If-None-Match header (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If...).
We experimented with something similar on a customer project where having a long-lived HTTP connection was not possible.