If you have the time I strongly suggest that you take some time and listen to the second edition of the openweb podcast. This episode should really be called the “Brendan show” because he does most of the talking. But if you’re into JS or you’re into programming languages in general it’s worth the listen. There’s lots of discussion of the trade-offs that went into the new ECMAScript Harmony effort and why ES4 and the ES3.1 efforts were rolled up together.
Arun also put up a post on the topic on the Mozilla Standards Blog that’s worth reading. But the podcast is particularly good. Especially if you want to know where the Web is going.