I tried out Postgraphile Realtime and it's pretty cool.
For anyone who wants something similar that's not GraphQL, then I'm in the early stages of developing a Phoenix (Elixir) implementation which broadcasts changes over websockets: https://github.com/supabase/realtime
https://docs.hasura.io/1.0/graphql/manual/subscriptions/inde...
https://www.graphile.org/postgraphile/realtime/