gsignond is now a weak dependency. While it's better, it's not perfect. Conflict of #1696927 remains.
With KDE already installed (with signon), when installing pantheon desktop we need to exclude weak dependencies :
sudo dnf install --enablerepo=updates-testing --advisory=FEDORA-2019-0f8dcf2a39 --setopt=install_weak_deps=False @pantheon-desktop.
This is not the expected behaviour as installing Pantheon Desktop aside KDE should be transparent to the end user without the need to explicitly remove weak dependencies.