Is there any EPEL impact to this? I don't know what is done there, but usually when we retire entire sections because they are out of date, we give a bit of consideration to whether those need to be moved into the EPEL guidelines.

That is a good question, which I am unfortunately well equipped to answer.
i am not involved with EPEL, apart from where it surfaces when contributing to Fedora.
However, the CMake macros come from package cmake-rpm-macros,
which is a subpackage cmake.
So I went to https://git.centos.org/rpms/cmake
and checked what each branch has in SOURCES/macros.cmake.
The macros are similar there, probably imported from Fedora at various of points of time.

• c7 does not have out-of-source macros at all
• c8s defaults to in-source
• c9 defaults to out-of-source

So perhaps an addition to EPEL Packaging,
saying that out-of-source macros are not available for EPEL 7 at all,
and that in-source is the default for EPEL 8?

I'm going to go ahead and merge this since there's really no point in talking about Fedora 33 now. The removed content is still in git and if it does still have EPEL relevance then it should be easy to pull into the EPEL-specific guidelines. It appears to me that EPEL could use some discussion or documentation of the cmake macros regardless of what happens with the Fedora guidelines.