1080p is 2073600 pixels 900p is 1440000 pixels 720p is 921600 pixels 720p to 900p......1440000-921600= 518400 pixels/921600= 56% increase 720 to 1080p......2073600-921600= 1152000 pixels/921600= 125% increase 900p to 1080p......2073600-1440000= 633600 pixels /1440000 = 44% So from just a 10% GPU Kinect reserve unlock and Xbox One SDK updates the Xbox which was barely producing anything above 720p has been able to achieve a 56-125% increase in pixel count when getting most of its current games to 900p/1080p. If all the Xbox One gets is a 5-10% increase in GPU power from a better optimized DX12 API then that should be more than enough to consistently achieve 1080p.
Let's look again at what DX12 is suppose to do:
1) PC it provides a lower level API to allow the software to talk directly to the hardware (metal). This will give PCs console level performance, in other words efficiency due to less overhead.
Xbox One already has a low level API so this won't really do anything but......
2) DX12 works better with command queues much better than DX11. On DX11 CPU cores have to wait in line to complete tasks. This slows everything down. With DX12 everything gets a chance to talk and distribute data simultaneously. This will help both PC and Xbox One.
3) ESRAM is a special type of memory that is supposed to work concurrently with DDR3 especially on high priority render targets. Early on developers pretty much ignored the ESRAM because they felt it was overly complicated and due to time constraints. A lot of potential bandwidth was lost because developers were shoving everything in the slow DDR3 pool. Now as more developers get the hang of ESRAM and there are better tools such as PIX to help optimize how ESRAM is best used with their render targets.
What does all this mean, specifically for Xbox One?
Well it means Microsoft build a box with DX12 in mind but didn't have everything ready from the jump, complicated by the fact the SDKs and drivers were an absolutely mess. Now everything is coming together, performance has jumped from the initial 720p offerings and developers are finally able to tap into the power of the Xbox One.
Does that mean DX12 changes hardware? No. It just means the API is going to maximize the abilities of the hardware its on. It is equivalent to somebody changing their diet to free themselves of sugars and fats, and hitting the gym. Your hardware doesn't change. The body is the same body you've always had but now it is running more efficiently. You're getting more out of it, because you given it better stuff to work with. Now if you go back and give it trash, your body will go back to looking like trash.