Apparently due to the systemd agenda of it's original maintainers,
ConsoleKit is "deprecated".

https://mail.gnome.org/archives/distributor-list/2012-January/msg00002.html

Consolekit2 is forked and actively maintained by XFCE4 maintainer Eric Koegel.

https://consolekit2.github.io/ConsoleKit2/

It works. Consolekit2 has been successfully deb-packaged and used here
(since even before Devuan) up to the latest "stable release" (1.0.2).

Is anyone interested?

David