The key point is that Android will never be on par with the latest version of Java. Scala has a lot of great features but its size and the learning curve is bigger than Kotlin. It's easier to start right now to develop with Kotlin instead Scala.
This far past the Oracle lawsuit and the increasing divergence between "real Java" and "Android Java", it is actually kind of bizarre Google hasn't really presented any kind of useful guidance on what they plan to do moving forward (unless their plan is actually to just keep limping along with a gimped Java implementation indefinately).
It is hard not to look at things like Swift and wish Google would make a similar push to update the "offical" Android language. Technically speaking, Kotlin is a great alternative, but without the sort of official blessing Swift has coming from Apple, for most developers it will be politically very difficult to get by the inertia that appears when suggesting you use a "non-standard" language, regardless of how interoperable it is technically.
Outside of really lean startups you might as well be asking to write your app in brainfuck if it isn't going to be in Java.
Oracle might have chosen some dubious arguments, but the reality is that Google forked Java and doesn't have any will to improve developer's lifes.
Before anyone replies how Jonathan praised Google, check Gosling history how things really went.
Gosling was at Sun until the end.
Sun just lacked the money to sue Google.