You can trick steam beta client to think that it's running under SteamOS by adding -steamos to launch options and then starting the BP mode. In the settings there is then option to "Enable Access to Linux desktop". http://i.imgur.com/jajsfNU.jpg
You can also probably just install any window manager you want.
Very interesting, although having dual boot you don't really need any of those things. I'm guessing the partition for SteamOS will be readable and writable from a Linux dual-booted. It takes restarting the machine but, who cares? And dual boot should definitively be possible.
I'm actually in the market to build a new PC in early 2014 and the compact-ness might just get me to get one of these. If the video card is a GTX 770 with a overclockable CPU, I'm in. All I would do is install an SSD, slap windows and dual boot into SteamOS when I play games and Windows to watch videos, write papers and do research.
Research on what? Use Linux! (In the line of the thread, I am disappointed)