Thank you for your input! We will consider this functionality in upcoming releases if it will be popular.
Everyone, please continue voting for this feature if you consider it important.
184 votesopen discussion · AdminSergey L (Director of Program Management, Plesk International GmbH) responded
Plesk supports PHP7 which is comparable to HHVM performance in many tests and in some tests even outperforms HHVM. We are recommending PHP7
This suggestion will remain open for a while, to hear your additional considerations in favor of HHVM