So we all know now that Apple has made it not possible to upgrade machines from Sierra to High Sierra using standard imaging. I believe High Sierra and later will still be able to be imaged, but going from Sierra to High Sierra is essentially like going from OS 9 to OS X. I just want to let people know that CloneDeploy can still be used if you build a NetInstall set instead of a NetRestoret set. This allows you still run a windows server running clonedeploy to deploy to macs. What's different about the 2 is that NetRestore would just copy an image down to the drive and call it a day. Well in order for any machine to run High Sierra, the client is required to do a firmware update that can only be triggered via an actual install. So that being said, just create a second Clonedeploy server and instead of creating a NetRestore.nbi use Automator or System Image utility to create a NetInstall.nbi. This will allow you to "netboot" your Mac clients to the actual High Sierra installer Via Netinstall and perform the upgrade. We also use Munki here where i work too, so we just add the munkitools.pkg to the automator workflow so that once the OS finishes installing, it installs munkitools and the client checks in with munki and pulls down and installs the required applications for the device. This is the best workaround i have found so far until we get all our clients to High Sierra where we can then mess around with testing imaging again.
Hope this helps,