I have been tracking NoSQL databases since early 2012, collecting publicly available data on skills and vendors. The NoSQL market is still tiny. Considerations and summary of data in Section 2 of this very large slide deck: speakerdeck.com/abchaudhri/considerations-for-using-nosql-technology-on-your-next-it-project-1 Slides regularly updated with new data as I find it. Data last updated in August 2016. Some of the past data came from InformationWeek when you used to publish annual assessment reports.