JavaScript is just another interface to Apple's "Open Scripting Architecture (OSA)." Previously, AppleScript was the only way to use it. The fact that they added another language indicates nothing about whether OSA will ever come to iOS. My guess is it won't; the new extensions APIs will likely handle any inter-app communication Apple wants to allow, because they are designed with iOS's sandbox model in mind already.
Put another way, Javascript is to AppleScript with respect to OS X automation, as Scala is to Java on the JVM. The existence of Scala does not indicate that the JVM will be ported to the Haiku OS. (There may be a better analogy but that's what I came up with.)