I see chances being even smaller to that. Dx12 does not only enable you to do more efficient programming by managing memory, it actually forces you to, which will be a new thing for many devs. And if they don't spend time optimizing, there's even less reason to go from dx11 to dx12 than to go from dx9 to dx11.
Dx12 is definitely a great thing, but what will it do to titles like AC:U, which could run flawless on 10 year old hardware if the devs didn't do an absolutely awful job at coordinating things efficiently.