I can't prove this, but I assert that a relational database that has solid JSON+text support (e.g. Postgres) is on much better footing than a NoSQL DB that attempts to implement a true relational model.
One is a adding a special new datatype, the other is trying to add an entire paradigm.
Just use Postgres. If you do need to migrate to Mongo for some reason, dumping your tables into JSON isn't the end of the world.