I recently created my own low-overhead binary JSON cause I did not like Mongo's BSON (too hacky, not mergeable). It took me half a day maybe, including the spec, thanks Claude. First, implemented the critical feature I actually need, then made all the other decisions in the least-surprising way.
At this point, probably, we have to think how to classify all the "JSON alternatives" cause it gets difficult to remember them all.
Is RX a subset, a superset or bijective to JSON?