Consider Hack Lang http://hacklang.org/. Perhaps it’s PHP’s brightest light. FB has put considerable effort to fork PHP and developer their own language + interpreter for good reason. Change is likely too slow or wouldn’t be made in PHP itself.

What your describing directly points to Hack Lang. Even their syntax is: <?hh

We should all take a look at Hack Lang (myself included). It could be what PHP 7 will be in a few years but is ready and available to use today. I'm watching this right now as motivation! (OSCON 2014: Include Hack - HHVM - PHP) http://www.youtube.com/watch?v=JrPGa1JDX38