They're rare in the US. KDE-as-default is close to the norm in Europe.
KDE has long been a more crossplatform system than Gnome (much better windows support (and even e.g. solaris), BSD is treated as first-class) so I'd hope they'll continue to avoid being systemd-dependent.
LxQt and any KDE-powered distro would beg to differ.
But I agree, in general, that KDE-default distros are few and far between. And the KDE team probably has better things to do with their time than try to maintain a systemd-less fork.