Skylake is the successor to Broadwell that's expected to be out in late 2015 but could slip into 2016. Skylake is expected to be more of a SoC design layout with the PCH integrated onto the die and will be launched in conjunctiuon with the Intel 100 Series "Sunrise Point" chipsets. Broadwell is expected to significantly boost the graphics capabilities over Haswell while Skylake will take the performance even further.
For several generations now, Intel has been openly working on their next-generation hardware support for Linux well in advance of the hardware's debut. This time is needed so all the necessary hardware enablement can make its way upstream, all code is properly tested, and the code incorporated into the major Linux distributions (ideally) before the hardware is released to the general public. For example, Intel released their Broadwell Linux graphics code last November and continues to be refined now for the past year in subsequent Linux kernel, Mesa, and xf86-video-intel driver updates. Ivy Bridge also saw open-source Linux support in the public domain about one year out.
With the Broadwell and Bay Trail Linux graphics support in good standing, Skylake is entering the focus of the Intel OTC graphics crew. It looks like for the Linux 3.18 (or 3.19) kernels is where we'll start seeing the Skylake Linux support emerge. A message was sent out to the intel-gfx list about new Intel DRM code available for testing. One of the items points out, "cleanup of the hsw/bdw ddi pll code, prep work for skl." Some Haswell and Broadwell code is being cleaned up in preparation for "SKL", a.k.a. Skylake. That prep code for Intel DRM testing is targeting the Linux 3.18 kernel for merging with the Linux 3.17 DRM changes having landed.
Hopefully the initial hardware enablement for Skylake will make it into Linux 3.18, which should be released by the end of the calendar year, and will then mature over the course of the next several kernel (and Mesa) cycles before Intel introduces the Skylake processors... There's still a lot of time to go. This is good news that it's already being worked on but should no longer come as a big surprise given Intel's big commitment to Linux support in time for the hardware shipping.
Stay tuned for Intel Skylake Linux announcements on Phoronix as the code starts to drop.