It's a smidge ironic that ESR himself is migrating a project away from it. :)
Eventually Mercurial ate Bazaar's pie and now Git is slowly eroding projects away from Mercurial. All hail Linus, who managed to create two open source systems that became de-facto industry standards.
With Linux it was the ability to use unix without having to stomp over to the university computer lab during the Finnish winter.
With git it was creating something that could handle merging patches from a disparate set of developers.
To some extent, it's good he's doing this. To another, very few VCSs other than SCSS can really be called "obsolete", just primitive. Most of the time, people who go on about VCS migrations seem to be just bikeshedding and can't seem to give out specific justifications other than listing features that the upstream project likely doesn't need. It's not trivial either, changing a VCS often means changing the entire way a project is structured, for often uncertain gains.
(I'd also say that atomic commits are an excellent reason to leave CVS behind, but that can be argued.)
you should never use a vcs that has no ability to ask "is this repo in a valid state", or you may try to checkout the point version released to a large customer and be unable to do so. Data corruption can happen, even on raid drives (we're pretty sure it was a bug in the controller, but that doesn't change the effect.)