It was a somewhat flippant (given that GitHub doesn't implement DNSSEC either) dig at the idea of using hand-entered/hand-updated IP addresses for access control, rather than having the access control system look addresses up in the system designed to securely attest owner/ip mappings.
(Almost nobody signs zones.) How is that any easier than just having an https:// URL from which you pull an (arbitrarily-formatted) list of IP addresses to block? Is the idea that you'd otherwise be able to do real-time DNS lookups on incoming IP addresses?
Yes - delay SYNs until an authenticated reverse lookup confirmed the IP was owned by a trusted domain. With caching to reduce common-case latency, which would otherwise be intolerable.
