[BeetleB]

>I will probably check it out, to be fair it seems unlikely to "unseat the incumbent" git

It will not, as they are more or less the same. People already on git have no good reason to switch. The only real benefit mercurial has is being friendlier. It may prove beneficial for new teams, but these days most people are already familiar with git and will put up with its pains (or rather, be oblivious to its pains).

Mostly an accident of history. If mercurial had initially gotten popular, I doubt anyone would be using git today.