I have, and I would recommend it, if it generated a Postgre schema from a GraphQL schema and not the other way around.
The advantages of GraphQL are its integration of backend and frontend workflows, and that won’t happen with PostGraphile: a frontend needing a schema change needs to go through the backend instead of the backend extending to meet the frontend in the middle.
Oh wait, we do have Prisma. And it suffers from those same issues.