> 4 bytes is actually too long for short messages

Would it ever be an actual bottleneck though? If it's not actually impeding throughput, I feel like this is more of an aesthetic argument than a technical one, and one where I'd happily sacrifice aesthetics to make the code simpler.

> some message can exceed 2^32 bytes

Fair enough, but that just makes the question "would 8 bytes per message ever actually be a bottleneck", which I'm still not convinced would ever be the case