I wish they would be implementing more of the runtime support in PHP itself. Why not make the FastCGI[1] code in pure PHP (like others have[2])? I understand if they don't feel PHP is the best language for daemons, but it would allow so many other developers to use, modify, and comprehend the implementation. I think HHVM suffers from a serious lack of dogfooding.
1 - https://github.com/facebook/hhvm/tree/master/hphp/runtime/se... 2 - https://github.com/kakserpom/phpdaemon/tree/master/PHPDaemon...