More details have been leaked on the next iteration of PCI Express. PCIe 4.0 is supposed to be able to handle double the amount of bandwidth as PCIe 3.0, boosting the number from 32GB/sec to 64GB/sec.
It's unlikely that GPUs will utilise this to its full potential but with more and more SSDs being built around the PCIe architecture we should see a nice increase in speeds. At Computex this year OCZ showed off some PCIe based SSDs running in RAID 0 and throwing out 3.8GB/sec.
Details are still scarce but we can expect PCIe 4.0 to be on the newest Intel Skylake boards running its 100-series chipset. That's all we have for now but we'll be sure to bring you more as it unfolds.