IMO Subversion was never as much of a standard as git. I saw a lot of software that still used CVS back then, and even more that didn't do version control beyond versioned source tarballs.

I'd be happy to be proven wrong. You won't get there by designing a solution that is more ergonomic (if jj even is), but rather by designing one that solves problems that git doesn't solve. Also, you probably need to get some big and important software (like Linux, for git) to switch to using it instead of git.

Even then, I'm usually _not_ an early adopter of something as pivotal as a VCS. This isn't something that's easy to rip out or rewrite later. It shapes my workflow at a deep level and holds the history of my changes in its database. Only once it's being used by 25-50% of projects I encounter daily will I consider moving stuff I control to it.

I have deep scars from mercurial lol.