I'm not sure what you're getting at. Is there reason to believe that this will not work with PHP >= 5.3?
It will be is not structured using Namespaces, which can be annoying if you are using them on a day to day basis and want to integrate something like Yaf that doesn't use them.
You could always write your own namespaced shim classes if it matters that much to you.
closures and anonymous functions, to my mind, were a jailbreak for PHP.