Visor Add-Ons That Make It Wearable?

afrazer asks: "Anyone know if one could make a springboard module to easily turn the handspring visor into a wearable computer? It would have to let you plug in an input device such as a twiddler and a heads-up display of some sort. Obviously this would not be the most powerful wearable system, but good for keeping tidbits of information handy." This is a good idea! Have handheld manufacturers investigated this kind of usage in any way?