Has anyone written their VCS plugin?

Forum_person: "I want to write a plug in for my favorite VCS ." TeamCity_person: "Wait until release x.y when we will support ]]>."
Forum_person: "Okie dokie"

I have seen this at least 5 times on this smallish forum, which leads me to believe that no one has ever really written this type of plug-in. I unfortunately have to work with a wildly unpopular and unknown VCS which will never be officially supported, so I am wondering if anyone has supported their own equally unknown VCS? The documentation is okay but far from complete and having a contact would be invaluable. Thanks.