You will be unable to use NetBoot with any model released on 5 Jun (Apple Store Sierra version is 16F73; OS build on new Macs is 16F2073)
I had to use System Image Utility (/System/Library/CoreServices/Applications/System Image Utility.app) to make an image of the new computer, and that image then worked with AutoCasperNBI. (That image should also work with AutoDMG; the big issue is that AutoDMG can only create a .dmg from an OS installer, and one cannot download/access an installer for 16F2073)
Summary: Download the Sierra 10.12.5 update for 2017 iMac (doesn't matter which 2017 hardware you are trying to netboot), add that package to the AutoDMG build using the same Sierra installer you can download from the App Store, then feed that DMG image into AutoCasperNBI and you have Netboot!
@matin.logmein I'm also seeing an incompatible recovery partition when laying down the image on 2017 hardware (when you attempt to boot to the recovery partition you get the prohibit sign). The recovery partition is listed when you run a diskutil list in Terminal. Any new information on this?