What is your setup now? I don't think it would be worth it to go with Haswell then the next year switch to Skywell just for DDR4. Plus how much do you think DDR4 programs will actually make full use of DDR4's bandwith. I have a feeling that when DDR4 comes out it will be like PCI-e 3.0 now. It's a nice idea but really nothing will make full use of it's greater bandwith.
It would be 2 years apart.