That makes sense to some extent, but I'm still unclear what real-world environment would exist where there is no server application to manage sessions, authorisation, and enforce data validation. And of course the scary "let's give all our users the complete source code of the application so they can modify it with Firebug to write anything they want to the live database."
Perhaps I am just used to thinking of a database as a big interchangeable repository of data and not an integral part of the application code. Even stored procedures are something I avoid.
I did however discover that you can create functional indexes on json data like this:
CREATE INDEX x_in_json ON mytable (jmember(jsonfield,'x'));
so I can see the point of being able to store certain types of data in this way and still have indexed access to it.