Note that "fall over" in the context of a mature RDBMS means that the database got slow because it wasn't properly tuned or administered, whereas in the context of NoSQL datastores, it may well mean "didn't write any data for the last five minutes, try to rebuild transactions from customer support tickets and your card processor's logs I guess????" or "woops, I just lost about $20 million in bitcoin". I think the potential tradeoff there is clear.