It is definitely interesting what is happening in the database space these days. It is good to see the NoSQL and NewSQL folks spark a fire under the traditional relational vendors. This is the only way to inspire innovation both in the commercial and open source space. To a large extended, the establishted relational player were slow to jump on the cloud and even to this day they are not moving as aggressively as they need to in order to reclaim the cloud database market from the NoSQL and NewSQL upstarts.
Fundamentally, the scale-out capabilities of traditional RDBMS engine still don't hit the sweet spot developers and cloud operations people need these days. I do expect the market will consolidate somewhat in the next several years as there are just too many players at the moment, especially on the NoSQL side. But I expect there to remain a large selection of NoSQL engines over time, as many of the NoSQL players target specialized areas so it is definitely not a one size fits all like it has historically been with relational database. For example, many of the NoSQL engines have made deliberate enginering trade-offs in their products such as in their storage models, consistency, replication, aggregation capabilities, and scale-out…etc. For example, if you need a NoSQL with strong aggregation functions you might choose MongoDB but if you need something that scales out writes and data center replication you might go with Cassandra. So, in the long-term I do not see a single NoSQL that can rule them all.