I mean, let's pick either 3.8 or master and only test against that. So then we end up with, say,

* PHP 5.2, WP trunk
* PHP 5.3, WP trunk
* PHP 5.4, WP trunk
* PHP 5.5, WP trunk
* HHVM, WP trunk

(HHVM we can worry about later though, since I don't think WP passes there yet)