Should they actually be blocked though?
I mean, it's a lot of relays, but they're also contributing actual exit bandwidth and it's not like they're spread over hundreds of /16s.
Maybe this calls for some dirauth-level patches to throttle families of servers to a certain CW?
I would vote for dirauth enforced families. Dirauths could put such relays into a family that has been defined by the dirauths, so that clients won't use more than one relay of that group.