Sorry for the delay in responding.
We are working very hard to exit BETA and move the PHP runtime to being Generally Available (GA) as soon as possible. We've recently released the PHP 5.5 runtime and a number of our most requested features (for example cURL, direct uploads and temporary files) and now we're working on ensuring that the runtime is stable and performant, as well as actively fixing any bugs that are preventing people from adopting the PHP 5.5 runtime. It is our plan to move forward to GA with the PHP 5.5 runtime and turn down the PHP 5.4 runtime.
BETA status refers to the fact that the runtime is not covered by and SLA and we may need to make backward incompatible changes before we leave the BETA release. That being said, it is unlikely we need to make a backwards incompatible change at this stage.