a relatively newish i7 or Xeon and 32gb ram will have you flying.
I find my even my i5 4690k @ 4.6ghz and 16gb ram, to be more than satisfactory.
it is true that some photo editing programs may use graphics cards in the future eg from pixinsight website:
GPU Acceleration
As of writing this document (October 2015), the current versions 1.8.x of PixInsight don't make direct use of Graphics Processing Units (GPUs). Hopefully this is going to change during 2016. We are working to implement GPU acceleration via CUDA programming on systems with NVIDIA graphics cards.
so it is perhaps maybe worth thinking about a little bit - or atleast making sure your power supply unit will be able to handle a GPU if you plan on adding one later.