This is the first release of the 8.x version of Imagecache External. All functionality has been ported, except for the link field formatter. If you don't need that functionality, this version is perfect as-is. If you do need it however, feel free to help out at issue #2684631: Port to Drupal 8.
In this release, support for blacklists has been removed. The permission flow has been simplified.
The path is configurable. Also, the module now defaults to the Unmanaged file system.
THe update contains an update_hook to leave the settings as-is. If you want to use the unmanaged file system or change the path in the files directory, you can do that in the interface.