One question and a random thought: What is the driving force for transport compression? Are you seeing that as a major bottleneck in particular circumstances? (I'm not disagreeing, just want to clearly define the particular problem you're worried about.)
Random thought: what do you think of defining this at the transport level rather than the record batch level? (e.g. in Arrow Flight). This is one way to avoid extending the core record batch concept with something that isn't related to processing (at least in your initial proposal).
