Why save it? Why commit yourself to a software program if you can do a superset of what it does with another, more robust, one?

I'd consider Subversion to be better than both Git and Mercurial if those changes were made (and implemented well). Subversion has a long history and plenty of tools already interacting with it that make it worth saving.

The whole point of SVN was to bring CVS up-to-date. People use it because, for whatever reason, they want a modern CVS. I'm not sure you can improve it without sacrificing the familiarity that's really SVN's primary asset.

Or we could just move on...