"as flash doesn't outperform JavaScript" does not imply that bytecodes cannot be faster than JavaScript.

Also, at least some people think bytecodes in the browser are worth pursuing (http://nativeclient.googlecode.com/svn/data/site/pnacl.pdf)

I think it will take just one popular app to make that client gain the desktop. It will be harder to take closed systems such as the iPad, but I think Google can pull that off, too (scenario: gmail, YouTube and the Google home page get superior, portable NaCl based user interfaces)