In the longer term, "semantic drift" might also be a problem. The article keeps referring to the example of the mayor of San Francisco. But the definition of mayor (i.e. what the job involves) changes over time, and the definition of San Francisco (i.e. precise boundaries, legal status) changes over time. Perhaps in this case there haven't been and won't be any major changes during the period of history we care about, but if you define millions of these QIDs there will presumably be a constant flow of awkward language-dependent questions about what they should refer to.