What could Oracle do if they changed their mind? Serious inquiry, IANAL, etc etc... I like to avoid speculating about the intersection of tech and legal issues, but is Scala in a very different place than other languages targeting the JVM? Are there any actual legal issues with writing a compiler that emits Java bytecode? This has been going on for a while, maybe as long as Java's been around. There's even some mention of it in the intro to the JVM spec.
Oracle could change their mind at any time. Some people at Sun appeared to be Ok with Android and sometimes even encouraged it.