That's not even the most ridiculous part.Yup I can't see a 100% performance boost on XB1 from DX12 unless MS gave the XB1 API development to 2 interns with a kegger and said 'have at it, your deadline is tomorrow by 5'.
Even if the CPU were to magically run twice as efficiently with an API update, the notion that you'd suddenly be able to double the resolution makes absolutely no sense. It's like people think that the Jaguar needs to do some kind of snazzy secret handshake with the GPU every time a pixel gets rasterized.