The shithole Google has dug itself and its developers is pretty deep, yet they keep digging instead of partnering with either MS (for C#) or Oracle (for real Java) to get a sane modern language.
But we'll end up with one of the following suboptimal solutions: - half-assedly backported Java 8 features (with buggy bytecode transformers for libraries that are included in binary form) - either Dart, Go or (why not go full retard) JS
When you see their Google IO presentations or interviews, they re-iterate that Java is the only true way on Android, with the NDK just for games and implementation of Java native methods.
Then the usual answer to standard Java support is "What features matter to you? Get in touch with us".
Is it so hard to see that who usually asks that question cares about 100% of the language or at very least the compatibility profiles?
Android N supports Java 8: https://developer.android.com/preview/j8-jack.html
That is not 100% accurate.
Android N has partial support for Java 8, it doesn't support all the new Java 8 APIs nor new bytecodes.
Additionally, given that Android M is around 10% after one year, how long do you think Android developers can fully target Android N?
Specially if they rely on APIs that did break, like JDBC interfaces.
Also Android Java isn't 100% Java as Google cherry picks APIs, which with the increase of Java 8's adoption is increasing the effort to write portable libraries that compile against Java and Android Java.
Also Android Java runtimes don't understand the bytecodes introduced in Java 7 and 8. So you cannot use libraries that make use of them.
This will only get worse with Java 9 modularity and with the value types, reiffed generics and new FFI planned for Java 10.