It’s my understanding that the current draft for DBOUND says that the lookup should start at the rightmost label (i.e. for www.example.com, com -> example.com -> www.example.com). Once a client encounters a record with the NOLOWER bit, the lookup process ends. This should prevent the owner of a domain under a public suffix from declaring itself a public suffix and thus bypass the rate limits in this particular use case (unless they specifically allow other public suffixes to live under said suffix). I’m definitely not an expert on this matter, maybe I misunderstood your point or the draft here.