As much of a Linux advocate as I am, I would be very hesitant about recommending it as the OS for this kind of build for a couple of key reasons that I don't see being resolved any time soon. However, under specific conditions it certainly would be viable, and in some ways preferable. The main problems that I see are:
- Graphics support is still shaky at best for Linux, although with the announcement of the Steam OS it is highly likely that we will see a surge in decent graphical driver development at long last. If you are going to build a Linux cab then I believe you will have better support with an ATI card. As Linus Torvalds once quoted quite publicly, "F**k you, nVidia!"
- Specialised hardware support for for things such as DMDs and motion sensors will be sparse at best. Doubtless such support will exist sooner or later as there always seems to be someone out there who has coded the necessaries, but will generally require a fairly high degree of technical voodoo to get it working. Even support and handling of multiple monitors, a standard in all linux distros these days, is still pretty shaky and temperamental in my experience.
- As has been mentioned, it limits you to a single game, but since Timeshock! is arguably the greatest pinball sim ever crafted by mortal man, I don't know if that's really a problem
On the flip side, Linux would be amazing for the following reasons:
- Cheap. You can use any existing spares or old machines you have lying around
- Much nicer for creating a streamlined, pinball-centric OS. Strip out the menu bars, desktop icons, wallpaper, and any unneeded daemons for stuff like bluetooth and wifi, and have it boot straight into the game. Very slick, and in fact exactly how a massive number of commercial arcade machines operate.
- Extremely fast to boot. My old Xubuntu install on SSD booted in about 12 seconds, plus add a few seconds for the game itself.
On balance, I would rather fork out the extra few quid to use something like a Mac Mini, which I know will provide me with excellent support and UNIX stability in a super compact form factor.