Instancing only works if the vertices of the objects be rendered are the same, i.e. the exact same object. The houses that autogen draws vary a lot in their appearance. You sure this is instancing that they are doing? I would rather guess they have tons of draw calls for the autogen cities and that this is the reason why DX12 will be beneficial.
Trees and grass are definititely instancing, but houses/buildings might not be from what I understand.