[annnnd]

I think parent was answering the usage of XML in this use case, which is not appropriate. XML has many strengths (as you have outlined), but it has also been (mis/ab)used so many times that it gained bad reputation. What my GGP suggests is an example of such. There is nothing to gain from XML here that any proper DB (with schema) wouldn't offer, or in this case, protobuf.

Kafka logs however are solving a different problem. The mental model is different - they do not record state, but the whole history of transactions, which makes it trivial to change the schema if/when need arises. Saying that the schema should be thought in advance and shouldn't change is not realistic IMHO.