It cant be. Json has a huge structural problem: it's an ASCII representation of a schema+value list, where the schema is repeated with each value. It improved on xml because it doesn't repeat the schema twice, at least...

It's nonsensical most of the time: do a table, transform values out of the db or in the consumer.

The reason postgres does it is because lazy developpers overused the json columns and then got fucked and say postgres is slow (talking from repeated experience here). Yeah searching in random unstructured blob is slow, surprise.

I dont dislike the idea to store json and structured data together but... you dont need performance then. Transferring a binary representation of a table and having a binary to object converter in your consumer (even chrome) is several orders of magnitudes faster than parsing strings, especially with json vomit of schema at every value.