Following discussion with several wallet developers, I have come to the conclusion that the secondary goal of managing labels in non-specialized applications must be sacrificed in order to achieve the primary goal of wide implementation across different wallets. While this tradeoff was perhaps inevitable, it was worth a try!
As such I have rewritten the specification to use JSON, specifically the JSON Lines format.
I understand some benefit of JSON Lines (JSONL) compared with JSON. But FWIW, Microsoft Excel (an example of non-specialized applications) support importing JSON file without macro.