To run python on WebAssembly you would have to compile the entire CPython executable, and every single dependency it has, into WebAssembly, then ship that giant executable with every page so you could then run Python code with it. You would then also most likely need a special library, which at some point someone will have to write or you'll have to write it yourself, to give Python a clean interface to the DOM. All of this together would be at absolute minimum 4.5 megabytes, which is absolutely unacceptably large for a frontend bundle.

WebAssembly is very cool techonology, but it's not going to deprecate Javascript because Javascript will be, at least for a very long time, the only scripting language that runs efficiently on the web, and also will always be the most well supported.

With WebAssembly you could write in any AoT compilation language that can compile on LLVM, but I, and many many other developers, have no interest in very low level languages like C, C++, or Rust in the browser, even though we acknowledge the flaws in JS. Maybe one day higher level languages besides Javascript will be practical, but that's a ways away.