I agree totally on all your points, and this still needs work, as I said.
But that age old boogeyman from the 90's of "javascript cryptography is flawed" has to go. It works just fine, and most of the complaints people have you can leverage against any language. Sure, it blows, but the SJCL has really good solutions to many of the encoding issues. After that it's pretty much just as lame as most languages.
Also, your attacks are valid on all existing sites, and I'm not claiming it solves any of those. If an attacker can get to the browser, then you're screwed always. I am not even trying to claim this solves any attack in the browser, and in fact I'm saying that all websites are vulnerable no matter what people use. Even with OpenID I can use evil UI tricks to get your password.
What this is solving is only the problem of people not wanting to setup their own auth system and get it right. It doesn't stop a determined evil web site from abusing it, because no solution would. It doesn't stop an idiot from using it wrong, because no solution would. It just helps them not store passwords, and that's it.