Intel has released a boatload of hardware documentation for Haswell's integrated graphics. This reference manual for open-source graphics programmers comprises thousands of pages covering pretty much every aspect of the current generation of Intel graphics. There are GPU overviews, register details, reference instructions, and memory views, just to name a few volumes. Even the graphics processor's general-purpose computing engine is exposed.
As Phoronix points out, this documentation drop isn't Intel's first. The chip maker has provided GPU details for years. It also offers open-source drivers through the Linux graphics section of its Open Source at Intel site.
News about Intel's graphics support for Linux wouldn't normally be that interesting. However, SteamOS has the potential to eventually make Linux the preferred platform for gamers. Intel's IGPs have grown increasingly competent in recent years, too. The latest Haswell incarnations can even hold their own against integrated Radeons. While it remains difficult to recommend an Intel IGP—or indeed any integrated graphics solution—for serious gaming, Haswell's onboard GPU delivers a good experience with more casual titles.
Haswell could also be potent enough to serve on the receiving end of the in-home streaming feature coming to SteamOS (and the Steam client for Windows). Valve hasn't published the hardware requirements for in-home streaming, but if Nvidia's Tegra 4-powered Shield handheld offers similar functionality, Haswell's combined CPU and GPU resources should be more than sufficient. Heck, even Bay Trail might be up to the task. Unfortunately, SteamOS only supports Nvidia graphics hardware right now. According to Valve, support for AMD and Intel graphics processors is "coming soon."