Michael Stonebraker on Current Developments in Databases
http://www.se-radio.net/2013/12/episode-199-michael-stonebraker
... says a "technology entrepreneur" who presumably has something to sell.
No-one gets rich if everyone uses a 30-year-old tried and tested technology that works reliably and is available for commodity prices. (E.g. MySQL and Postgres are free). However, the lack of vigorous marketing does not mean that it is a bad idea.
I sometimes think that it would work better to store question definitions in the question bank using a NoSQL approach, rather than the current multiple relational tables. (e.g. it would make full-text search easier). However, since all the rest of Moodle uses a relational approach, I think it would a bad idea for one specific area (the questoin bank) to break that pattern.
Arguably, blocks have alwas taken a sort-of 'NoSQL' aproach (since before that buzz-word existed) with the block_instances.configdata column storing a blob of data, rather than using a normalised database structure for those settings.
NoSQL is not panacea and I'm not advocating that current Moodle switches to NoSQL. I'm just thinking about future. Moodle can be scaled but it is a pain to do so because of the way it is built. If full power of horizontal scaling is to be achieved Moodle needs to be completely redesigned internally, and at least partially nosql could be part of that effort.