To be honest, we love PHP7. However, certain functions that are needed for site profiling + many existing themes & plugins don't as yet exist in PHP 7, so our advisory to WP users is to wait.

Site Speed Profiling is the ONLY feature out of 6 speed up features in Optimiser that is not supported in PHP 7 (yet) so rather than turn that feature off to make our product PHP 5/7 compatible we decided to keep it open for PHP 5 users (81%) as it's really useful.

We are keeping an eye on the new PHP rollouts as it's the most requested update - we WILL do it as the PHP call required are there.
FYI PHP5 & PHP7 are independent versions that have been running side by side for years & both are being updated... it's not like other software where the former number is immediately deprecated & other than some neat features in 7 the only other difference is a minor improvement in speed in certain situations...