I would say that there will not be one, at least not for now. The populus does not seem especially interested in better than CD sound. Add to that the fact that the music companies are going to try to hang DRM on any new format and I think new formats are not too likely. I stopped buying DVD-A's and non-hybrid SACD's because of the DRM. I am not going to spend a lot of money on something I can only listen to in my living room. Plus they weren't that much better. I remember the revolution CD's were over vinyl and cassettes, in many ways. It was obvious why they caught on. It is going to take lot to equal that.
With the progress in digital storage it is conceivable that very high def music may be so cheap to produce and store that the CD will just naturally die off as something that is hopelessly antiquated. But I just don't see the impetus driving this. Again, most people don't seem to care, and "most people" are the market.
