The angst towards DX12 in this thread is amazing.. DX12 will become an industry standard whether you like it or not, and it will benefit gamers across multiple architectural platforms, something which Mantle could never do..
After some consideration, I have decided that DX12 is more similar to Mantle than I had previously thought. We all know that Microsoft had plans to port the Xbox One's low level API to Windows, so I now believe that DX12 is a more refined and expanded version of the Xbox One's API, enhanced for multi-architectural support and backward compatibility..
Those of you saying that DX12 is a rip off of Mantle are clearly delusional. It is more likely that Mantle was AMD's sole attempt to port the Xbox One's low level API to Windows for it's GCN based GPUs, rather than Microsoft merely copying Mantle.. AMD could never have created Mantle without Microsoft's blessing, seeing as it borrows quite a bit of technology from D3D11..
Also, as DX12 runs across multiple architectures and is backward compatible with DX11, it must have taken YEARS to formulate and finalize the standard, as something like this obviously doesn't occur overnight and requires the input and cooperation of multiple IHVs...
Yes, Mantle will get it's time in the Sun, but since it's architecture exclusive, it's simply not in the same class as DX12 when it comes to importance and will eventually die out as DX12 gains a solid foothold.
And DX12's market penetration will occur much, MUCH faster due to the main performance benefits being fully backward compatible with DX11 hardware. If DX12 is released for Windows 8/8.1, which I think is very likely, I would expect performance oriented DX12 updates and patches for DX11 games starting in the first half of next year, with full blown native DX12 games in 3rd or 4th quarter when Windows 9 arrives..
Mantle is serving it's purpose, which was to make AMD more competitive with NVidia in the short term, and serve as a unique feature with which to attract gamers.. But it was never intended as a long term solution..