It would be interesting to see white/black-lists on individual lookaside repo.

That way components from external repos can be filtered before joining the main "gather" bucket.

One option is config like this:

gather_lookaside_repos = [
    (variant_uid_regex, 
        {arch|*: 
            {
                "url": repo_url,
                "exclude": ["coke"],
                "include": ["wine"]
            },
            {
                "url": repo_url,
                "exclude": ["cake"],
                "include": ["pie"]
            }
        }
    )
]

Another way might be to support yum/dnf .repo files, and honour the exclude= lines in those files.

First step is to find out if pykickstart actually supports specifying repos as URL to .repo file. If not, then some backwards compatible change to config will be needed.