At the presentation of this work at PETS last week, the Tor developers said it was useful for understanding the nature and scope of this behavior, but their intended long-term mitigation is to completely change the HSDir protocols using additional privacy mechanisms so that the directories know much less about the records in the directory (and about who is looking up or connecting to what). The developers don't believe it's going to be a reliable solution to police directory abuse on a case-by-case basis, so they want to see a protocol change instead.