How do you feel about something like CBOR? In which stage would you say it's stuck in evolution compared to ASN.1 (since you said Protobuf is still TLV)?
CBOR and JSON are just encodings, not schema, though there are schemas for them. I've not looked at their schema languages but I doubt they support typed hole formalisms (though they could be added as it's just schema). And since CBOR and JSON are just encodings, they are stuck being what they are -- new encodings will have compatibility problems. For example, CBOR is mostly just like JSON but with a few new types, but then things like jq have to evolve too or else those new types are not really usable. Whereas ASN.1 has much more freedom to introduce new types and new encoding rules because ASN.1 is schema and just because you introduce a new type doesn't mean that existing code has to accept it since you will evolve _protocols_. But to be fair JSON is incredibly useful sans schema, while ASN.1 is really not useful at all if you want to avoid defining modules (schemas).
I was considering CBOR+CDDL heavily for a project a while so they're a tad intertwined in my head. I very much liked CBOR's capability of being able to define wholly new types and describe them neatly in CDDL. You could even add some basic value constraints (less than, greater equal, etc.). That seemed really powerful and lacking ASN.1 experience it sounds like a very lite JSON-like subset of that.
