Lua, a programming language I think might appeal to Pythonistas, is in a solid position to profit from the compile-to-JavaScript fad. I did some tests with mherkender's lua.js[1] a while back and Lua translated to JavaScript was only taking around 40% more time (I forget the exact numbers) to run the horrible benchmarks I wrote. There's still low hanging fruit to improve those numbers. Lua is a beautiful language. In addition, it's the language with the best chance at making it into a browser engine. It's lightweight - the compiled binary is around 120KB.
I'm not sure that Lua is going to appeal so strongly to Python programmers. It's wordy and its design makes opposite choices from Python's; vide global vs. local, for example. I think the brevity and safe assumptions of Python are a lot of what people value in it.
Thats if you only focus on syntactic issues like that. If you see how the languages work they are actually much more similar (both have generators, operator overloading, lexical scope, etc...)
Using any syntax, "local unless you specify global" and "global unless you specify local" are different in an important way. And syntax is important to most programmers; there are dozens of languages that provided the semantic equivalent of Python before it existed, but haven't matched its popularity. Python's practical syntax is much of the reason.
> Lua [is] the language with the best chance at making it into a browser engine
For better or for worse, I think there is pretty much 0 chance of Lua or for that matter Python showing up natively in browsers. There are too many technical and political things in the way.
But we already have good tools for compiling both of those languages into JavaScript. If for example the Python community made JavaScript a priority to compile to, we could make it run very well and integrate nicely with the browser environment.
[1] https://github.com/mherkender/lua.js