(it's Protobuf, Hive account@cm-steem :))

The only downside I can think of is that it's binary so it's more difficult to read off the air. I use Protobuf at work to publish data from a microcontroller to an Android app and a web service. Doing that in text with lexical interpretations would be a nightmare.

To further compress the binary serialization we could use 16 byte binary representation of the CPIDs instead of using it's hexadecimal form. I suspect that's where a lot of the storage goes.