Custom feeds can be also be carefully and manually crafted by the owner, this is the basic and obvious option I envisioned and talked about after the Eternal December that blew up the Global and our following lists as well.
If a list is good enough that the owner updates and follows it, it could be a good inspiration for his followers, so it can be easily forked and personalized; maybe the clone could also check for "upstream updates" from the original one and treat them as suggestions to merge.