One of the NetBSD developers is a Mercurial developer and I think the general plan for a while has been to switch to Mercurial once a few technical issues have been fixed. I'm not sure if that has fully happened now and it is just waiting on the right people having enough time or what the status is. I think NetBSD and OpenBSD are the last two actively maintained open source projects that use CVS, at least as far as I am aware.

However, at least for NetBSD (don't know about OpenBSD) there is an official mirror on Github and you can submit pull requests there if you want (I'm fairly sure this will stay the case even after a switch to Mercurial). Some of the main developers mostly use git until a commit is almost ready. I think the main practical difference from the project using git as the main repository for anyone who doesn't have commit access is that while commit messages will mention the contributor I don't think it is linked on github to the contributor in the same way it would usually be with an accepted pull request. At most there might be a tiny number of extremely minor issues with the repository conversion left, and I think those might have been fixed by now as well.

If it works for them why not, and compared to rcs it's really not too bad ;)

In some aspects the old centralized versioning systems are superior to distributed systems like git (for starters, they give you a single linear history with incremental revision numbers).