Update on iPartition. Over the weekend I used v. 3.6.2 to convert the 1 TB internal flash drive on a MacBook Pro running Sierra (10.12.6) from case-sensitive to case-insensitive. As noted above, you have to make a separate bootable disk with iPartition on it. Since recent macOS installs require so much room, Coriolis Systems deleted the option for generating a DVD for boot several versions back. I used an external clone of my system drive.
Since you are booting off a new disk, you have to re-activate iPartition after rebooting, so make sure to copy the license image (a png with a QR code on it) over to the external bootable drive as well as the app.
Once booted on the external drive, it was simple to select the filesystem for conversion, uncheck the box for "Case Sensitive", and click Go. After maybe 15 minutes, it was done. Rebooting off the internal drive worked fine, as did all of the apps I tried for a quick test.
A few caveats: iPartition does not currently support the new AFS, so it will NOT run on High Sierra (10.13). It does not support CoreStorage, so if your drive in encrypted by FileVault 2, you have to turn off FileVault and wait until the decryption process runs to completion before you start. If you have a Fusion drive, you're out of luck. Also, it warns you that if you have any files in a directory with names differing only by case, it will rename one of them as part of the conversion.
All in all, it was a fairly easy process, and well worth the price of the software.