How about bundling Mercurial with SmartGit then, so a new SmartGit comes with a compatible Mercurial?

Yes, but it's an absolute pain when SmartSVN (on Mac) decides to update itself to 8.0, then announces that your supported Hg version (3.4) is no longer supported, and directs you to the Mercurial site, where you download 3.9, and then SmartSVN says it doesn't support 3.9 yet and you need 3.7, but the Mercurial site doesn't have 3.7 available. This is a nightmare.