At the moment, the only fully supported language, and the de-facto standard for DOM tree manipulation in the browser is JavaScript. It looks like it has deep design issues t
Many people understand that Javascript isn't best and prettiest language ever. However, it is currently supported by browsers, and thus it will be extremely hard to introduce a different language. We simply don't need another browser war.
This explains why I know of no plans of switching to a different client-side language.
But I think Javascript isn't so bad if you start thinking about DOM model and how would one work with it. Many things that are messy with JS are the result of the way DOM model works.