Update Feb 10: I asked Activision if the easter egg is a permanent addition to the map throughout Black Ops 7 or whether it will depart when the Winter does. An Activision spokesperson told me: "We're happy players have discovered the easter egg on Rebirth Island. Players who want to get their hands on the blueprint shouldn't wait to hunt it down for themselves." Vague, but reading between the lines, that makes me think that it'll be time limited. So best not to wait too long!
