Copying a proposal by @Kerry_Raymond from the advisory board mailing list:
Would this allow us to set up a hierarchy of rules for automatic citation? First, use the one in my user space if it exists and succeeds, else use the one in the community space if that exists and succeeds, else use Citoid, else do the minimum {{cite web|url= ... |title=Unknown title |access-date=today}}
This would be nice as it would allow individual users to precisely control the citations of URLs of importance to them (presumably ones they use regularly) or to test new rules without disrupting the community's use of existing rules. It could also be potentially extended to enable more complex cascading, e.g. alternative rules in different languages, WikiProject-specific rules, etc.
Probably not something for the minimal viable product, but it never hurts to have ideas for future extensions on the table so early design choices don't frustrate later development and to mark points in the code base with comments "this is where we'd deal with SuchAndSuch"
The Web2Cit-Core is already prepared to use configuration files from different storage locations (as used by the sandbox endpoint of the Web2Cit-Server), so it should be ready to support this use case in the future.
I just wonder to which extent this would discourage collaboration around a single set of configuration files.