People avoid introducing new data stores because it adds complexity and it's harder to do queries across data sets. Jamming different data models together in on

People avoid introducing new data stores because it adds complexity and it's harder to do queries across data sets. Jamming different data models together in one system is a very viable strategy. Postgres supports functional indexes, so indexing individual fields within a JSON document is already possible. If it's not easy now it will be easy soon. Remember XML databases? They became extremely marginalized when relational systems started adding basic support.