I'm also really excited about Rust. What would be unimaginable exciting would be if Rust has any plans for iPhone or Android devices. Preferably without a 10MB runtime and a decent debug story. Elsewise, absent the runtime,F# is the most interesting language closest to fitting that bill.
There will still be churn, but it's much smaller nowadays; once we hit 1.0 we will be committing to backwards compatibility.