I’m happy to answer any questions.
Every other day I wonder: how much usage is Scalafix getting? Maybe it’s too early, but at some point it seems we’d need to get adoption at scale before relying on it. At least, “it works on 90% of the community build so we can just deprecate all these old features in next release—say, 2.13.x”—but even better would be seeing projects configured for it.
It’s being used for Cats 0.9 to 1.0 upgrade (pr currently in progress but looks great so far https://github.com/typelevel/cats/pull/1793) so that is some current indication of usage on a well used project. My hope is that as users see how well it works out it will become more popular. No idea how many are using it internally as I did at my last job (and will continue to at my next gig) but I would also love to hear more people give a mention if they have used it successfully.
Scalafix user adoption is still quite low, scalafix-core got ~700 sonatype downloads in July. The last releases have had some sharp edges around the integrations (esp. sbt-scalafix, but also how to share/consume rewrites), which are partly addressed in the upcoming 0.5 release. I am continually testing it on larger projects, and plan to automate at some point the currently manual tests where I run scalafix on parts of the community build.
I am personally very excited to see cats v1.0 migration succeed!