The last few updates to Microsoft’s DirectX platform have come with the requirement that you get new hardware to enjoy the benefits, but that’s not going to be the case with DirectX 12. According to Microsoft, DirectX 12 will work with most existing gaming hardware, at least for the most part.
Basic feature set will work on NVIDIA's Maxwell, Kepler, and even Fermi, as well as AMD’s Graphics Core Next (GCN) architecture. Basically, a DirectX 11.1 card will be compatible with most of the new APIs. Note, Maxwell is actually the first GPU with full DX12 support.
While past updates to DirectX have focused on new rendering effects like tessellation and more realistic shaders, DirectX 12 is an attempt to dramatically reduce driver overhead. Some of the more significant aspects of DirectX 12 will be included in the basic features including power efficiency and frame rate improvements.