x11-misc/sddm does not add its user to the video group. I've tracked it down to a bug in the ebuild syntax. When calling enewuser, it should be this: enewuser ${PN} -1 -1 /var/lib/${PN} ${PN},video instead of this: enewuser ${PN} -1 -1 /var/lib/${PN} ${PN} video
Thank you! Should be fixed in: commit cec1882183eee8385b9d4b3b13a04c1fc2201860 Author: Manuel Rüger <mrueg@gentoo.org> Date: Mon Aug 29 12:08:10 2016 +0200 x11-misc/sddm: Add user to video group, fix QT dependencies Gentoo-Bug: 592116 Package-Manager: portage-2.3.0