In a language where the rules are defined by what one implementation does, once an alternative implementation has the necessary critical mass, that becomes the language.
If I remember correctly, Facebook was submitting PHP patches for a long time, especially when they concerned security.
And once there's 100% parity between HHVM and Zend's interpreter, why would I, as a user, care whether the competitors are working on the same product?
Honestly, by creating a spec and a new implementation from scratch, Facebook has done far more (in far less time) for PHP than Zend has in the last 5+ years.
