> niche Linux distros that would be cut out including everything from Gentoo to Alpine Linux and Slackware.

Gentoo lets you choose the init system (including systemd) so it doesn’t belong in this list.

Gentoo belongs to the list, because it will be strongly affected if KDE will become more dependent of systemd in the future.

Gentoo attempts to provide independent choices, e.g. one should be able to use KDE with either systemd or OpenRC, or XFCE with either systemd or OpenRC, whichever the user wishes.

If KDE will become dependent on systemd, then the possibility of free choice will be removed from the Gentoo users, so they will have to decide which is more important for them. As a Gentoo user, using OpenRC instead of systemd is certainly more important for me than using KDE instead of another desktop environment, so KDE will become unusable for me.