Haven't looked at it in detail, but have you mentioned docker builds?
I see you wrote about mock, which is immensely useful for building RPM packages.
But docker seems well-suited for this task, for example:
https://github.com/alanfranz/docker-rpm-builder
I hadn't gone down that far into the rabbit hole yet but I'm absolutely open to adding new content around using docker for rpm building. Thanks for the feedback!
What's your take on this?