Avro makes that case slightly better because you can default value for a missing field in one of the two schemas and then it works. It's not worth the boatload

Avro makes that case slightly better because you can default value for a missing field in one of the two schemas and then it works. It's not worth the boatload of problems it bring in all other and normal use cases though. Having the default value in the app or specified by the protocol is good enough.