Would it be feasible to write a PHP equivalent to emscripten, so that one could export software compiled from any frontend language (including, e.g. the WASM representation) as a php object that can be run directly by mod_php?
It should be possible, but I'm not sure if PHP has the kind of community drive behind it to make it a realistic option.
Or a necessary one – emscripten's main use case is "everyone has a browser", but there's very few PHP hosting offerings where you can't shell out and just run straight native code (in your own little isolated sandbox).
