No one can say for sure what Prismatic is doing behind the scenes since it is a commercial entity but I've seen them speak at a couple conferences, which led me to believe they are doing some pretty novel ML studies. I could be wrong. But, your initial point was to suggest that a company shouldn't use anything other than Python when starting new ML projects, and Prismatic is an example of a company doing just that: using Clojure in this case. The article you mentioned earlier gives some good reasons why Python is often not the best choice for ML: speed, security, portability are often the reasons for leveraging the JVM (where Clojure lives). This is not a knock against Python, just pointing out that there is major stuff happening in ML that has nothing to do with Python. NYU's machine learning lab prefers C++ over other languages, and major projects like Siri and Watson rely a lot on C++ and Prolog. The point is that it makes no sense to claim that Python is the only language anyone should consider for these tasks.