As snprbob86 pointed out, that already exists: Pyjamas @ pyjs.org.
I used pyjamas a while back for a couple toy projects. It's quite nice and sounds like what you're looking for.
With Skulpt, I wanted to avoid the build step that Pyjamas has (the compiler's written in Python, not Javascript so you run it ahead of time) and at least when I used it, it sometimes felt like Javascript with Python syntax, rather than actually programming in Python. It's certainly closer to Python than Skulpt is today though!
I'd actually love to create a "GWT like" that would compile my python (in javascript/html/css) for the different browsers out there. That would be awesome.
GWT is nice and all, but python >> Java...