Whiptail is part of the package newt, which is not included in the Fedora 28 boot iso. Since the upstream distribution is based on Fedora 28, I'd assume it will not be part of the OL8 final image.
However, rebuilding the boot ISO using lorax is very straightforward, so newt can be easily added to the installer.
Thanks for the reply. Indeed whiptail is part of the newt package and is available in all the OL7 boot images as we use whiptail a huge amount during our kickstart builds. Not having it available in OL8 during the kickstart boot / build phase will not be acceptable to us as a huge Oracle partner unless there is an alternative to it that is just as easy / lightweight to use that does the exact same functionality.
Ideally we do not want to have to rebuild the boot ISO etc every time.
There is also no mention at all in the OL8 documentation that this feature is no longer available to use during kickstart builds etc.