CI is slowly migrating its jobs from Precise/Trusty instances to disposable instances running Jessie. In order to migrate the jobs depending on HHVM to Jessie, we would need a HHVM package matching the one we have for Trusty.
Not much of a priority right now since CI is not migrating PHP based jobs right now. We fir need bits to be able to select which flavor of PHP (Zend 5.3, Zend 5.5 or HHVM). We are not there yet.
So merely filling this as a reminder we will have to package HHVM for Jessie eventually.