I'd also add that SPA[1]/client-side applications are also an important consumer of databases with decent JSON support.
The "backend" for these types of applications are often relatively thin API wrappers around a database, with the bulk of application logic on the client-side.
Postgres' JSON improvements over the last couple of years have made it a pretty good choice already for these sorts of things, but the JSON indexing improving would make this a no-brainer.