The colission in question is /usr/bin/xembedsniproxy, which suggests xembed-sni-proxy is made superfluous by the new plasma-workspace. Reproducible: Always
Thanks, fixed in git by Andreas. https://gitweb.gentoo.org/proj/kde.git/commit/?id=2b17a8c3045a236a3931d59ac9cddd03ae72bc2b