I like your proposed rule change, Chris. Having a Wikipedia page could be used as a criterion, though it's not perfect. Wikipedia's notability standards are rather picky. It would probably be close enough, though.
We could just come up with criteria as we go. Eg. for now, we could say political leaders of countries are historically significant, regardless of when they were born. Then we could add to that if we come up with other examples?
Brian: Regarding why we single out HSAs, it started out with user groups forming to take care of the many duplicate profiles that existed of these people. And I agree with you that this applies regardless of time in some cases. While with the Acadians, for instance, most duplicates are of the 300+ year old profiles, there were lots of duplicates of Queen Elizabeth, too, and she's still living.