The expected behaviour is to depend on virtual/jack. Do you have any particular reason to depend on media-sound/jack-audio-connection-kit instead?
1.18.2 is out and still depends on media-sound/jack-audio-connection-kit
commit 28172396344923a67ee2a0aa25ee6f29a3956aef (HEAD -> master, origin/master, origin/HEAD) Author: Lars Wendler <polynomial-c@gentoo.org> Date: Mon Oct 2 12:21:21 2017 media-libs/openal: depend on virtual/jack (bug #626868). Package-Manager: Portage-2.3.10, Repoman-2.3.3