But... NPCs do sort of romance each other? We all know what happens at the party, and there's flirtatious party banter on top of that.
That was early access...it might have been a planned feature that just got cut or it could simply be no more than that...banter. At any rate they have now confirmed that in the full game that NPC origin characters cannot romance each other...only players can actually initiate and advance romances with party members.