Yeah, the issue is that Python is pretty hard to sandbox, being the hugely dynamic language it is. I imagine it would take a lot to get the browsers to stop working on their JavaScript implementations that they have sunk insane amounts of time and effort into, and start something brand new.
Trust me, I'd love to see it happen, but I don't think it will.
Automatic type conversion, NaN is a number, NaN doesn't equal itself, leave off a 'var' and you start creating globals, "0" == false but "false" != false, parseInt assumes that anything beginning with a 0 is octal, anonymous functions everywhere (which discourages code reuse), there is nothing that even approaches a decent looping structure, etc..., etc... - I'm no expert, I fully admit, but what I have used of JavaScript makes it quite clear that there are huge problems there.
Really, I'd be happy to take another look if someone could show me why everyone loves it - but even without the mess of DOM and HTML (which I agree, are half the pain of web dev with JS), I don't see it.
The Tao is like a glob pattern: used but never used up. It is like the extern void: filled with infinite possibilities.