Cockpit is rudimentary and hardly worth the time. And as far as I can tell, there's very little interest in expanding it from the broader community, as the lack of plugins would seem to indicate.
I use it solely to give a webui for managing virtual machines on individual servers.
It hooks into libvirt for this, so I can also manage them via virsh et al, but it's a nice tool to set up the essentials of a VM and provide remote access to the VM console.
It doesn't have a patch on Webmin, sadly.