two points;
1) How do you get the disc into the optical drive through the clear plastic?
2) I thought about a similar idea when the mini was released. The idea being that there would've been good to release the mini with a modular design where the base unit was the mini cpu less the optical drive (ideal for networks in schools etc I would think), then on top with the same dimension (except height) you could add the optical drive of choice and on top of these other modules could be added at will. Maybe an extra hard drive or drives or elgato TV type device or airport/ADSL modems etc. You'd end up with a column of various devices joined with docking ports or you could have a perspex tower to slot each item in and out with out moving the other again with docking ports in the tower to save any wired connectors.