The MKI used polycarbonate and aluminium for its case. Polycarbonate is well known for being bloody tough and easily worked, perfect for when you have no idea whether things are going to be flying off at you and you need to throw something together quickly and cheaply. The downside is that it tends to pick up and retain scratches and marks.
Since I am fairly confident that the PCB itself will not disintegrate or have components pinging off I decided to instead go for a pre-built acrylic 5mm edge glued 400mm cube. While not as resilient as polycarbonate, acrylic still has a significantly higher impact resistance than regular glass and far cheaper for one off prototyping than some of the more advanced glasses (tempered/laminated).
If the Kickstarter reaches its funding I am going to investigate the possibility of either switching to either a custom formed acrylic enclosure formed of two semi-spheres or a cube of toughened glass/acoustic.