I really don't think this means what some think it means. Read the DF Architect's interview :
http://www.eurogamer.net/articles/digitalfoundry-the-complete-xbox-one-interview
"Digital Foundry: DirectX as an API is very mature now. Developers have got a lot of experience with it. To what extent do you think this is an advantage for Xbox One? Bearing in mind how mature the API is, could you optimise the silicon around it?
Andrew Goossen: To a large extent we inherited a lot of DX11 design. When we went with AMD, that was a baseline requirement. When we started off the project, AMD already had a very nice DX11 design. The API on top, yeah I think we'll see a big benefit. We've been doing a lot of work to remove a lot of the overhead in terms of the implementation and for a console we can go and make it so that when you call a D3D API it writes directly to the command buffer to update the GPU registers right there in that API function without making any other function calls. There's not layers and layers of software. We did a lot of work in that respect.
We also took the opportunity to go and highly customise the command processor on the GPU. Again concentrating on CPU performance... The command processor block's interface is a very key component in making the CPU overhead of graphics quite efficient. We know the AMD architecture pretty well - we had AMD graphics on the Xbox 360 and there were a number of features we used there. We had features like pre-compiled command buffers where developers would go and pre-build a lot of their states at the object level where they would [simply] say, "run this". We implemented it on Xbox 360 and had a whole lot of ideas on how to make that more efficient [and with] a cleaner API, so we took that opportunity with Xbox One and with our customised command processor we've created extensions on top of D3D which fit very nicely into the D3D model and this is something that we'd like to integrate back into mainline 3D on the PC too - this small, very low-level, very efficient object-orientated submission of your draw [and state] commands."
This is why we shouldn't expect miracles. Consoles always have good 'closer-to-the-metal' access to hardware, and of course this was a big focus when getting the XB1 ready. DX11 to DX12 on PC will be a pretty sizable leap in some areas thanks to things they've already done on XB1's version of DX. Microsoft have confused things with the naming, but think of it this way :
PC DX11 = DX11.
XB DX11 = DX12.
PC DX12 = DX12.
XB DX12 = DX12.1
The reason is that the big penalties with generalized hardware (draw call limits due to CPU) were ALREADY fixed on XB1. So the best we can do is look for tweaks in the area, but not miracles.
