Couchdb isn't exactly the best thing to judge NoSQL by today especially by it's old performance issues, lack of automatic compaction, indexing on demand instead of proactive background indexing, etc.
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.