Well, software firms have already been using some variant of VCS for a while. The legal world needs to first get sold on the concept (at least on all the bits beyond Word's "Track Changes" functionality), and then... well, nobody but techies looks at VCS based on richness of CLI commands, or depth of mathematical foundation, or provenance / industry cred of its authors -- lawyers will want something with reasonable GUI UX; whether it's powered by Git or Mercurial or whatever, doesn't really matter.
(FWIW, I think embedding Git support in MS Office would do a lot towards VCS adoption outside of tech.)