Well DirectX 12 already takes care of everything mantle did and more, the only advantage right now is mantle already being implemented on some engines, curious to see what they are going to do with it next.
Disappointing, they should have released the SDK past year. Now it's too late, and I think they know it.
Let's see what this means
Mantle’s definition of “open” must widen. It already has, in fact. This vital effort has replaced our intention to release a public Mantle SDK, and you will learn the facts on Thursday, March 5 at GDC 2015.