I think that NoSQL databases are a really interesting set of technologies, however they aren't necessarily a panacea for many problems, including scalability. There are likely some problem domains where a particular NoSQL technology might work better than an RDBMS, and perhaps some situations where many types of databases would work well.

I ran across a piece that looked at some of the complaints that companies have with NoSQL technologies. It's a generic piece, perhaps too generic, since a graph database is not like a document database. However it does talk about the issues that companies see, such as performing analytic queries. While a row-based RDBMS isn't ideal for these queries, often the platforms work very well for a wide variety of reporting requirements.

I do think some of the problems people have noted have to do with the maturity of the systems. There are a lack of references for how to run a high uptime NoSQL database, not many data models to review that may or may not work well, and relatively few administrative techniques to maintain these databases. The problem isn't that NoSQL databases can't meet your needs, or run quickly, or provide many 9s of uptime, but rather many enterprise professionals might not know how to find the information to accomplish these goals. That's something easily solved across time.

Ultimately I think the NoSQL world has a lot of maturing to do, and we, as professionals and media, need to start to differentiate among the various flavors of databases. I am glad to start seeing articles and blogs refer to graph databases when they cover a product like Neo4j rather than writing NoSQL. Slowly I am seeing MongoDB referred to more often as a document database, not a NoSQL database. It's good to start to separate technologies and not confuse one with another.

One thing in the piece I did notice is that it's likely that we will see more platforms and products incorporate both RDBMS and non-RDBMS technologies together. We see that in SQL Server already with the addition of columnstore technologies in the last few versions and Polybase to SQL Server 2016. I expect we'll also start to see some of the capabilities of DocumentDB added to SQL Server, along with, perhaps, graph based technologies in the future.