In systemd-208-28.fc20.x86_64, /usr/lib/kernel/install.d/90-loaderentry.install contains a bug breaking parsing of /proc/cmdline. This prevents kernel install from ever succeeding if there's no /etc/kernel/cmdline. The bug was introduced upstream in 2f3a215f61d758cd59b3be5b65976a12401ac4ff and fixed in c008f6ee8df9aa36782378d1a3767543b3635a54. Please cherrypick the fix to Fedora 20.
http://pkgs.fedoraproject.org/cgit/systemd.git/commit/?h=f20&id=c392b042458b24dccd6aed8cfd81f84fb3aa4cde
systemd-208-29.fc20 has been submitted as an update for Fedora 20. https://admin.fedoraproject.org/updates/systemd-208-29.fc20
Package systemd-208-29.fc20: * should fix your issue, * was pushed to the Fedora 20 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing systemd-208-29.fc20' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2015-0254/systemd-208-29.fc20 then log in and leave karma (feedback).
systemd-208-29.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.