I've spent most of my career, actually most of my life, working with relational database systems. I tend to agree with this piece on NoSQL systems being the wrong tool for many applications. I do think that's the case, though to be fair, I haven't done anywhere near the amount of work on key-value stores, document databases, graph databases, etc. as I have on relational systems. I admit I'm biased, but I think the author is as well. He works at MemSQL and used to work on SQL Server.
The piece notes that relational databases didn't deal well with certain problem domains and various NoSQL classes databases evolved to handle the challenges. The good things about this is that relational databases were forced to grow and adapt, incorporating new features and functions. I do truly wonder if that is the reason we've seen rapid changes in SQL Server, both in capabilities and the pace of new releases.
Many of the non-relational systems are built to incorporate transactions, but usually within a very limited range. For example, many document databases only allow ACID compliant transactions within a document, not across documents. The same might be true in graph structures. Many of us working with relational systems know there are often a decent number of queries that need transactional consistency across entities, and sometimes across different databases. Our applications demand this, and while it might be overkill at times, it's a capability that is definitely needed.
There is also a discussion of schema-less features. I do understand the attraction for application developers. Adding or changing the way data is stored is much easier when there isn't a set schema for writes. This truly does make development easier. What it doesn't do, however, is remove the technical debt of having a schema. Instead, this debt is pushed to the reader, and often, means the application must maintain the ability to apply some schema for reads to make sense of the data. Does that mean everything needs a hard, strongly defined schema? No, but I think it means we need some schema.
Ultimately I think that there are problem domains best solved by different platforms. In most cases, I'd argue a relational data store is the better platform, but I am certainly willing to entertain the discussion of where a graph, document, or other data platform may work better. Just be sure you argue for the problem being solved. Most of us aren't operating at the Google/Facebook/Spotify/Netflix scale, and we have different problems to solve. We need something that works well for our problem, not the one another organization is facing.