In reply to M.
HHVM had its moment in the sun but Facebook never added the developers to increase compatibility with the outside world. We had some big sites on HHVM and the ongoing small, niggling but site crippling bugs drove us back into the waiting and friendly arms of true open source PHP 7.

HHVM quick rise and demise in the WordPress world is a case study in how not to take over an open source niche (benign neglect).