I recently implemented a similar (simpler) format https://baremessages.org/ in ruby.

First thoughts are:

ION pros: - easy to skip around while reading a file - no need to write a schema - backed by amazon so major langs will have impls - good date support - better concatenation, probably better suited to logging than bare

ION cons - what's the text format even for?

BARE pros: - schemas keep things tightly versioned - smaller binaries (not self describing like ion) - simpler to implement so tons of devs have impl'ed for their favorite lang - better suited to small messages (think REST json api)

BARE cons: - no skip read - no date support

I might do an ion ruby implementation too, to really feel out the difference.