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.