In yesterday's announcement of the Bay Trail SoCs finally coming to market with the Atom Z3000 series, all of the talk was about these Atom SoCs with graphics formerly known as "Valley View" being run on Google's Android or Microsoft's Windows 8.1. While modern Intel hardware support more or less implies there will be Linux support, and Android support is just a step away from supporting the Linux desktop, there should indeed be decent Intel Atom Z3000 series support for standard Linux distributions.
On the graphics side, their Open-Source Technology Center for months have been working on the hardware enablement under the Valley View codename. In fact it was through public Git commits in how Phoronix was the first publication to report on a new Atom SoC coming with Intel graphics bearing an Ivy Bridge class graphics core rather than continuing to push Imagination PowerVR SGX graphics onto the Atom package.
With Mesa 9.2 and the Linux 3.11/3.12 kernel, the graphics support should be in pretty good shape. I don't yet have any engineering samples or review units for Bay Trail hardware, but from my communication with the upstream developers and in monitoring the commits for months, this is what appears to be the case. There may be some initial bugs or performance not up to par with Windows, but overall it should be in good shape. Intel uses the Mesa driver on Android too, and with the Atom Z3000 mobile focus, their Linux Mesa driver is high priority.
Beyond the graphics core, Intel already committed TianoCore support for Bay Trail (and even Broadwell). Within the GCC and LLVM/Clang compilers is also Intel Silvermont support for being able to take advantage of the CPU instruction set extensions the SoC has to offer by using the GCC 4.9 or LLVM/Clang 3.4 compilers with the "-march=slm" compiler flag.
The Linux 3.11 kernel also brought Intel Bay Trail audio support and other changes pertaining to future hardware enablement.
While I can't guarantee the Linux hardware support or performance until getting my hands on some Bay Trail hardware in the months ahead, at this time it appears to be in pretty good shape if using the Linux 3.11 kernel or newer along with other parts of the updated stack: Mesa 9.2, the latest Clang and GCC, etc. When tablets and other Atom devices start arriving, there will be plenty more details and coverage on Phoronix of the exciting low-power SoC.