It is interoperable. Keychat relay only add collecting bitcoin ecash function. If the relay operator provides free service, current relays e.g., Damus relay can be used as Keychat relay. The android apk will be released first, then the code.

Keychat message is also kind 4 event. So Keychat can use all relays which supports kind 4. The difference between Keychat messages and DM messages is encryption/decryption methods, which processed in client. Relays don’t care about encryption.