I'm far from an expert on this topic, but I am a developer, and I am currently working on a project that leverages both MySQL and ElasticSearch for storage. MySQL handles all of the "boring" data such as users, profiles, comments, etc. ElasticSearch is basically a giant product database, no real relational data, just a normalized structure and easy to query. ElasticSearch is serving as a primary data store, there is no backing in a database because ES is just that good.
Whenever I see these "SQL vs NoSQL" arguments, I always have to wonder: Why one over the other? A lot of projects can benefit from both and there's no reason you absolutely HAVE to use one or another. It's perfectly reasonable (and probably ideal) to use more than one storage system in your projects.
If you have a bunch of nails to hammer in and bolts to tighten, you don't choose just a hammer or a wrench to do that job...you grab both and use each for what they do best.
I agree that using Elasticsearch as a primary data store seems risky. The situation is improving though; the v1 release introduces easy backups (for example, to s3) which from my experience work very well.
Whenever I see these "SQL vs NoSQL" arguments, I always have to wonder: Why one over the other? A lot of projects can benefit from both and there's no reason you absolutely HAVE to use one or another. It's perfectly reasonable (and probably ideal) to use more than one storage system in your projects.
If you have a bunch of nails to hammer in and bolts to tighten, you don't choose just a hammer or a wrench to do that job...you grab both and use each for what they do best.