At what point do I get to tout out the No True Scotsman paradox? Every NoSQL solution whether as its own DB or built into another one (like Postgres) I've worked with I've either hated (Couch, Mongo, Cassandra, Neo4j), or relegated to _very_ specific use-cases (Riak, Redis, Postgres).

I agree with the Wix team. I've used Mongo in a very high volume site and it was a constant source of headaches. We even had an engineer we called "MongoDB" because he was constantly having to deal with scaling it. It didn't even handle more than 10% of the application data, it was strictly for timelines; the rest of it was in trusty old MySQL. If we'd just done blobs as JSON in MySQL in the first place we would have been completely fine.

Even though I prefer Postgres, knowing nothing else, I would prefer 100% SQL in MySQL than a Postgres backed application that splits the storage between tables and KV store.