Choice of development language is realistically more of a business decision than a technical one. With the proliferation of REST APIs, there are no longer really any technical hurdles to using any language.
Scalability can be an issue, but honestly business scalability is a problem for most businesses long before technical scalability is. Ruby and Python are awesome, but it can be hard to scale a company with one of those languages because it's hard to find good programmers who know Ruby or Python. It's much easier to find good Java or C# developers.
At this point, given all the work the Apache foundation has done to make Java awesome, I don't really know I would consider another language from a business standpoint. Sure, from a technical standpoint Java isn't that exciting; but it's easy to scale, easy to hire for and relatively standard across a number of platforms. Java code is also relatively easy to maintain since it forces you into certain design patterns.
There are some domains where this wouldn't hold true (and data science is definitely one of them -- you'll have an easier time hiring a machine learning expert who knows Python than Java) but that's really just technology. In a production environment, you'd eventually wrap your Python code in REST APIs and write all the ETL and interface code in Java.