I had imagined that the table would just be defined in advance from a src file. That would be consistent with other comparable features arc offers. And the memoization would just be a code efficiency thing.
If we don't care about being consistent, it certainly would be cool to have the table load from a data file, and then to have the first run of an override write to file when it's not present. Memoization to, again, cover code efficiency.
As for use cases I only had a few plural overrides I needed to deal with and I too just hard coded them. At the time I did so I remember thinking I should put it in a table, but never got around to it. Then I saw your post and I thought of it again!
Note that I don't really use arc these days, but I have ported most arc functions over to clojure and I'm always looking to improve my library. In my clojure world I would just store them in datomic as facts. I think I might run along and do this now that I've spent some time thinking about it ... ;)
