I was truly hoping that RethinkDB would be the Mongo that Mongo could have been: a NoSQL database, but one with joins; a NoSQL database that is
actually CP [0]; a database that comes out of the box with granular real-time updates (so you don't even need to worry at first about the extra moving parts of a Redis server or other queue). For a business starting from scratch with those needs, I'm making do with Mongo, but I was anxiously waiting for RethinkDB to get more battle-tested... alas, it wasn't meant to be. And I fear that we'll be stuck with Mongo for quite a while.
The truth is that NoSQL has great promise, but the folks with actual money to spare today are the ones who want a better SQL database, because they can afford the tradeoff of development time for reliability that SQL administration and migration provide. And people who solve the SQL pain points, such as the excellent folks at CockroachDB, and the various folks building replication layers on top of Postgres, can hopefully keep the market for database startups alive long enough for someone else to fix the NoSQL landscape as well.
[0] https://aphyr.com/posts/284-call-me-maybe-mongodb , where one finds that Mongo actually isn't guaranteed consistent during partitions, actually did hit us in production, and we had to dig through a rollback file manually (shudder); fun times. On the other hand, see: https://aphyr.com/posts/330-jepsen-rethinkdb-2-2-3-reconfigu...