Wow! I was under the very wrong impression that memcached hadn't been updated in a long time. It has been having regular releases for longer than I thought. Great to hear!
My major use-case for a KVS is *reliable, scalable* storage. RDBMS has an upper bound on scaleability. Removing the relational component removes a lot of power and flexibility, but improves performance and scalability.
That's often a good choice!
A KVS can be arbitrarily horizontally scaleable. That might not sound necessary for a small project, but even there:
1. You can deal with big data (e.g. keystroke-level event data, etc.)
2. You don't have to worry about scaleability. It's one less thing to worry about.
3. You're set up for success if you take the unicorn route.
That's not memcached. I like memcached, but it's not the same as a KVS.
https://memc.rs/intro