3. There are lots of cool things to do with them [relationship designators]. In any event, you have to determine the substance of a 1xx/7xx to the work in order to catalog it under any code, so adding an appropriate $e shouldn’t be too traumatic.
This ignores the reality of dealing with it all, such as: how many libraries today cannot deal with the current changes in the authority headings. What does this portend for the future of the relators? Sure, there may be cool things you could do with the relators IF they were input in a way that is pretty-much consistent–but when 99.99% of all of the millions of records do not have the relators, and the fact that each record can have three or four (or more) headings that would need relators, plus the fact that they are not required in new cataloging, then the reality is that you can do cool things with less than ,01% of the database.
Not very cool.
If relator codes are to be useful and really cool, they will have to go beyond mere display and will require searches. Retrospective conversion of the 99.99% of the database that does not have relator codes should not just be ignored. It is the entire herd of elephants in the room that everyone is pretending not to notice. Dealing with that mass would demand a complexity of analysis and an outlay of resources that would make the current updates to the RDA authority headings look like nothing.
So, although we could add the width of every item we catalog, or the color of the cover, or when I cataloged Russian books, I could have added “Proletariat of the world, unite!” whenever it appeared on the title page, it may not have been that much extra work. I have no doubt that people could imagine “cool” uses for that information, but the need still remains to demonstrate some kind of utility for the public and that it is worth the expense. Otherwise, it is just a matter of catalogers adding loads of superfluous information. And thereby undo the “cataloging simplification” of the last several decades.
But I guess adding them makes some people happy. That is the only reason I can guess.
Finally, looking at the list at http://www.loc.gov/marc/relators/relaterm.html could be rather traumatic for some…