Javascript would be an obvious choice for anything centered around creating UIs. Palm-now-HP's nice WebOS platform is essentially a recent direct competitor to Android and did that.
I really don't think a dynamically typed language is desirable as the primary development language for a mobile platform. Static typing is just too useful and makes it a lot easier to optimize too. Java is still quite a bit faster than JS.
Something like Kotlin seems like a good choice to me, if it takes off.
