You're correct that the Scala version isn't ABI-compatible. But Scala doesn't care about ABI between minor releases anyway, so that probably wouldn't stop them

You're correct that the Scala version isn't ABI-compatible. But Scala doesn't care about ABI between minor releases anyway, so that probably wouldn't stop them from changing it to align with Java. There is also precedence for this, Scala 2.12 changed the encoding of lambdas from anonymous classes to Java 8's invokedynamic.