We actually use https://github.com/supabase/walrus to get the database changes and we're planning on moving to a Rust worker (https://github.com/supabase/walrus/tree/worker/worker) for better performance especially in the RLS-enabled use case.
I promised José that I would check out Postgrex.ReplicationConnection and we might add it in to our Supabase Realtime some time in the future.