This is a valid point, but hits on something that constantly grates with me. We already have something massively more cross platform and performance focused than JavaScript - C. The problem is that the standard library for C is utterly lacking, and there is a lack of focus on developing mechanisms to deploy native code /directly/ across the web.
Don't kid yourself either - all the data being thrown around at the moment is always (always, always, always otherwise it wouldn't even work!) translated into native code in some way - we are already throwing native code around the web, just in a horribly inefficient way. In todays world of sandboxing and virtualisation all of the security arguments that used to be completely reasonable are quite thoroughly invalidated.
I really do believe that fixing this from the technical perspective is not an impossible or even hard problem to solve - I can not stress this point enough. Game developers are constantly re-solving this problem in limited, optimisation focused ways. JavaScript implementations themselves are ultimately built on top of this technology or other technologies built on top of it. The standard libraries of modern scripting languages are possible to use from within the constraints of C. We have already solved all of these problems and there are myriad examples.
On the other hand, the political problem could be intractable... and thats sad.
Worst of all perhaps, C can be made better for performance without much thought or effort, and none of the new languages I see actually tackle this problem, which is quite real and measurable and impacts everything from productivity to the environment - they (quite rightly in many ways) focus utterly on ease of use and massive standard libraries. Why can't we focus this effort on fixing C, or providing a better alternative?
Why are we trying to catchup with native code performance instead of using just native code? Why aren't we improving native code performance in a serious way?