The typesafe deal, use of SBT and other scala tools, and the overhead of maintaining docs and bindings for 2 languages all seems to point to an inevitable deprecation of Java at some point.
Hopefully not?
The "engine" benefits from Scala, as a highly concurrent and transactional heavy system. The choice of language for building MVC applications & services on that engine is left up to the developer. The 2.0 mindset, and you see this in everything is very much a best tool for the job balanced with flexibility and choice.
It's going to take a little while for a language like Scala (or any JVM based language) to fully penetrate the market. A lot of Java developers are not there yet, and by a lot, I mean most, who are we kidding. I see more shops embracing the JVM as their "stack" and the right language for the job mindset on top of that foundation. It's flexible, conservative, and forward thinking at the same time.
Play fits nicely into that space and is something that the core team appears to be mindful of. In fact, if they're smart about it, Play could end up being a bridge for Java developers interested in making the transition to Scala, at a pace that makes sense for them.
I just think it will be hard to justify play2's use in java-heavy organizations if Java support is a second citizen to Scala.
I loved Play 1.2.x, I think it is the only framework that really provides a way forward for modern java web dev, and I strongly hope Play 2 keeps things moving.
By a wide margin, the overall consensus in the JVM community seems to be that Scala will probably never be more popular than it is today, which means, it will never become mainstream. Hopefully, one of Ceylon or Kotlin will succeed where Scala failed.
With that in mind, Play betting on Scala is quite a risky direction indeed.
I'm seriously asking, not trying to challenge you.
Taken in isolation, these numbers don't mean much but when you start putting all the evidence together, it's hard to make a case that Scala is growing at all.
also, play is not "betting" on scala. Just because it was implemented in scala and provides a scala API that does not mean you can not use the framework from Java (or Kotlin, or Jruby etc.). If you do not care about the scala API, that's fine, use the Java API instead.
HTH