draft-ietf-v6ops-nat64-pb-statement-req-00.txt says:
R11: IPsec support.
The translator MUST support communication between IPv4 node and IPv6
node using UDP Encapsulation of IPsec ESP Packets as defined in
[RFC3948] as applicable. RFC3948 should be interpreted as with the
IPv6 side on the IPv6-IPv4 translator being the IPv4 private side of
the conventional NAT. IPsec support MAY require updating also the
IPv4 side.
Actually, I think the real requirement is that both IPsec and IKEv2
work. IPsec without key management is pretty useless in practice. Is
that what is meant?