To be blunt I don't believe Mercurial has reason to still exist. It's feature advantage over git is very marginal at best, and it simply lost on popularity. If you ignore the inherent value in popularity (popularity means you spend less time training new hires who aren't new to the industry), then Fossil wipes the floor with Mercurial and Git in terms of features.

In my view, the legitimate choices for FOSS version control these days are git (good enough, and popular) and fossil (featureful and obscure.) Why you would ever pick mercurial instead (marginally better than git, but almost as obscure as fossil) is completely beyond me. It occupies an uncomfortable middle ground of mediocrity.

https://www.fossil-scm.org/index.html/doc/trunk/www/fossil-v...

(The one caveat here is that Fossil may not be appropriate for very large scale decentralized projects, but frankly that's a problem git and mercurial are solving that most companies don't have.)

(Incidentally, editor extensions for git have almost eliminated my CLI interaction with git. The UX of vim-fugitive is great, and similar extensions exist for just about any modern text editor. I think CLI UX is becoming less and less relevant when it comes to version control.)