"2.1.1.4 Cons
Unbalanced cost is a ground for DDoS. Though this protects against enumeration, it is not really a path for versioning."
This should also mention the security risk of the requirement for an online key.
Which you could add are of particular concern where not all secondaries are under the same administrative control as the primary (whereas with DNSSEC-bis this is irrelevant)
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