I've also been around long enough

RCS provided revision control CVS provided concurrent checkouts by different users Subversion allowed moves and renames and atomic commits git is distributed.

Each one of those was so much better than the previous one that it replaced the previous one, despite that previous one being ubiquitous.

Mercurial might be 5% or 20% better than git, but it doesn't matter. It's not 300% better.

Mercurial won't take over after git, in the same way KDE won't take over after Windows. The next thing has to be the iPhone - the thing that changes the paradigm completely.