AFAIK, Hadoop is converging on Avro -- not sure about the state of each component within Hadoop with respect to avro, but in long term, I expect it will be the protocol.
Patches have been rolled back, commits vetoed, and the direction seems to be providing a pluggable thrift/protobuf/? RPC option, which seems weird to me. In any case, there was a lot of back pressure to avro.
Also given it's complexity I dont think I can recommend it in the RPC area.