DX12 will take off when Nvidia wants its to take off. If Nvidia wants its to be dead than it will be dead no matter how much people like it or hate. AMD can only be audience and watch Nvidia to decide the faith of DX12.
I don't think Nvidia really care either way at this stage. They give plenty of support to DX12,their GPUs have more DX12 features than AMD at the moment, and they are porting gameworks to DX12 so its not like they are ignoring it. They are marketing a little as way to get people to upgrade but they realize that develops don't really care for it at all and until windows 7 user base is small enough there is not going to be a great change