I have to agree with @BYK, there's been a lot of interest in getting PHP7 compatibility added. Multiple individuals have offered to work on getting 7.1's async working in Phabricator going back to pre-7.1 release. Phabricator contributors have consistently been absent from the discussion or just shut it down. It's stifling progress and causing interested developers to take their talents to other projects where they can actually get things done.

PHP 7.1 RC2 is now available, and the patch for async_signals was merged into what is presently the 7.1 branch.