I agree with Mike Pall's view. And the current crop of Javascript engines proves that too. Simplicity wins over complexity.
Although I still hope pypy will deliver on its promisses. We have to bear in mind that pypy's goal is not just enhanced speed. Its goals are much broader and this is one reason why, perhaps, this is not the best approach if you want full speed (there are trade offs which seem acceptable considering all the other benefits, such as easier of implementation of dynamic languages on top of pypy's framework).
Although I still hope pypy will deliver on its promisses. We have to bear in mind that pypy's goal is not just enhanced speed. Its goals are much broader and this is one reason why, perhaps, this is not the best approach if you want full speed (there are trade offs which seem acceptable considering all the other benefits, such as easier of implementation of dynamic languages on top of pypy's framework).