I don't get it.
For every customer which has access controls configured based on IPv4 (sounds crazy enough already), GitHub would configure a trivial DENY ALL policy for IPv6. Problem solved.
that's the scenario they want to prevent. they can't force the client to use ipv4, if they connect via ipv6, they will be served an accss denied.
that's the scenario they want to prevent. they can't force the client to use ipv4, if they connect via ipv6, they will be served an accss denied.