Well thing is Story has not considered Core at all when they made Nu.
But Core is an Evil-Lawful faction and Core's premise is both boastful domination over Omicrons and and monopoly over Omicron based Resources. They already have a monopoly over Iridium, being left out of Nu altogether with Azurite Reactor and massive relics and Nomads etc. threatens their goals.
TL;DR: Devs forgot about Core, instead did the boring Order-Navy-Zoner thing. There should be Core presence and tensions at least. Liberty's presence is weak, Core's presence should exist in some capacity.
Open war is player RP of course and has no chance to get into story. Core presence and tensions? Well, they really should be included. At the very least it would lead to Liberty+Core vs Order in canon with some legal tensions between Core+Liberty when their scouts/charters/explorers meet and don't fight nomads/infected ships/Order.
