As you know, PostgreSQL introduced Json(b) support at the 9.4 version [1], and hstore v2.0 saved in separate repository [2]. But although PostgreSQL has this support at the core level, there are many useful functions, which wasn't ported to Json(b) from hstore v2.0 and json. Here [3], I've made a review of the missing Json(b) functions, which can be implemented. This list can be updated in the future, of course. I want to implement the missing functions in the form of extension (e.g. contrib/jsonx).