Great article.
But I think Asynchronous Programming can already be done in PHP with the pecl extension pthreads (using other syntax), doesn't it?
pecl.php.net/package/pthreads
"Backwards Compatible Mode" seems inviable, because some features just could not have a simple syntax like comments (use of class with generics, for example).
In any case, I think PHP could adopt some optional improvements and walk beside the hack quietly.