The main feature of DX12 is the performance especially in terms of drawcalls, which I think would really benefit an MMO. It has also been shown that porting dx11 engine to dx12 is fairly easy task.
However for some reason SE gives the impression that priorizing content means that engine programmers are somehow 100% involved in that. I mean sure I would want content first and extra graphics stuff later but why couldn't we have both? (Seriously SE give me that damn AA)