Earlier quoted context omitted.
I assumed everyone would be encouraged to just convert their json columns to hstore if they wanted the extra speed, being as theyre equivalent. What would be the reason for funding JSON-as-binary?
Traditional databases use complicated indexing and storage structures in part to minimize the need to examine unrelated data. hstore is better than plain text for JSON but a scheme closer to the existing PostgreSQL table/page/row/value hierarchy could be better still. I'd recommend reading the recent post https://news.ycombinator.com/item?id=6813937
Of course if I need it to be eye-wateringly fast I wouldn't be using a document store. I'd use good old relational or something like redis. Often though you just need a sensible place to put some unimportant schemaless key-value data without a half dozen extra dynamically created tables or whatever. EAV makes me very sad.