Primal's relay is just another relay with a different protocol.
They serve views with this instead of querying relays directly: https://github.com/PrimalHQ/primal-caching-service
Then they got bullied hard for that and added the ability for users to choose their relays. But I'm still not sure if the clients actually connect directly to those relays, or just add it as an extra parameter to their service. Either way i think their idea was valid all along.