Regardless of Kotlin (which I don't feel inclined to learn at this point), would you say Scala is usable for Android development? I'm about to start a personal project and would love to use Scala if possible. Note: by "usable" I mean really usable, not "it works, but with lots of caveats and extreme pain" :)

I needed to write a very simple Android app a few months ago and decided to use Scala. This was my first and only experience with Android development, so that may have had something to do with it, but I wouldn't recommend using Scala for any serious project. It took me a ridiculous amount of time to get a functional dev environment, and I probably spent the first week fighting with the tools. I finally got IntelliJ IDEA set up to where I was mostly happy with it, but I never managed to reach that final 10% of functionality—for instance, I never got the IDE to auto-compile on save, which meant I had to keep an SBT session open and couldn't reliably use the IDE GUI for running the app. (Sometimes the two would compile at the same time and I'd get all sorts of weird errors that could only be fixed with a clean.)

Having said all of that, once I got everything working, I felt that using Scala was worth the pain. Programmatic layouts using scaloid gave me a vastly better experience than coding them in XML, and implicits worked really well for passing around the Context object. The tooling just wasn't, by any means, reliable, so I wouldn't recommend it for any apps your career depends on. :)

I haven't tried it, but I've heard that Kotlin is a nice compromise if you're looking for a language nicer than Java with more reliable tooling than Scala.