Without it the welcome dialog is always shown, even after selecting the option to not show it again. The other options might not be saved either, I haven't checked. Installing kde-frameworks/frameworkintegration as suggested in https://bugs.kde.org/show_bug.cgi?id=362082 fixes it.
Thanks, fixed in git. https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=b29a231662e6f79bca695307ff9663e558021462 https://gitweb.gentoo.org/proj/kde.git/commit/?id=16c52e20bb9c8feedf7ba585232a599d83f4ee1d