The kickstart files (that are baked into the ISO) in simp-core are different between the EL6, EL7, and EL8:
If EL6, EL7, and EL8 really require different kickstart files, then each major EL version's ISO is missing the file templates needed to kickstart agents for the other two supported major EL versions.
This is particularly relevant to SIMP 6.5.0, because it supports EL8 agents, but a SIMP server no higher than EL7. This would mean that a newly-installed EL7 SIMP 6.5.0 server could not use the ISO-provided files as a template to kickstart EL8 agents.
We already have a ticket to package the kickstart files in their own RPM. This would allow versions for different OSs to be available at the same time, regardless of the OS version of the server on which the package is installed. Also there is a ticket fix the YUM repo directory structure of the SIMP repos to better support kickstart servers that support multiple OS versions. These tickets should be considered when we design a solution. However this work may not be achievable in the 6.5.0 timeframe.
No, that note refers to the OS packages, and hand-waves away other details with "There are notes throughout the instructions to help in setting multiple OS but they are not comprehensive." That much is true, but even with those notes, there is no way for a SIMP administrator to know what the content of another OS's pupclient_x86_64.cfg should look like, or if its diskdetect.sh or repodetect.sh should be different or how.
could you link to those tickets? The RPM approach sounds promising. An alternative that would be easier to document and use (particularly for automating PXE tests) would be to provide a templating tool (something like `simp kickstart new [OPTIONS]`) to handle the configuration and validate against common problems.