At work our internal Chef infrastructure has been using an older version of Chef for a while. We built out several fully Chef-managed internal projects, all using an automated CI/CD pipeline for running Kitchen tests and pushing cookbooks out. That work's been in maintenance mode for a while, everything's been functioning as expected, and we haven't added a lot of new services or features. So there's been no strong motivation to keep investing the time to upgrade to new Chef versions.
Now Chef 12 is hitting end of life this month. This brings a minor concern of only limited support for any issues we come across in our own cookbooks in future, and the larger concern that the community cookbooks we rely on may drop support for Chef 12 so we won't be able to use any new features they add.
I'm going to start working on updating at least our core cookbooks to newer Chef versions. My plan is to start with updating from where we are now, Chef 12.14.89 from Sept 2016, to Chef 12.22.3 released about a month ago. That should give us the deprecation warnings needed to make things compatible with Chef 13.x, hopefully without critically breaking many things.
Once that's updated and rolled out across the board we can (hopefully easily) look at bumping up to the latest Chef 13.x, or maybe jumping straight to 14.x that comes out later this month depending how different things look there.
We'll see how it goes...