I got it running on my HP pavillion Chromebook 14 (stable) in developer mode using croutonized debian jessie (64-bit). It works but I'm not exactly sure what I'm going to do with it :)

The XDK itself is available for Windows, OS X and Linux. When you go to the download page (http://xdk-software.intel.com/) it detects the OS you are using and provides you with the appropriate download. At the bottom of the download page are links to download the XDK for a "non-detected" system.

The XDK operates identically on all three platforms, one of the reasons for using node-webkit to create the app.

Interesting. I just assumed since it seems to have detected that my Linux machine is running Windows. The fact that they were using node-webkit did make me surprised that it appeared to be platform-specific.

They are just targeting the 95% of developers.

While there are certainly a lot of developers using Windows, I'm skeptical that it's as high as 95% given the number of developers using Mac OS these days.