We've optimized key sizes to have as few press molds as possible and to make it easy to handle the stock. Since all the keys are changeable and can be outfitted with displays, it's not a good idea to have 'right control key' and 'left control key' to be different parts (and part numbers).
Space bar is one of its kind. Then come three others: regular key, middle-size key, and double-size key. That's it.
Here's the preview of what we'll show at CeBIT this month (to be released in the end of 2007):
Return and Shift are double-sized, Alt and Ctrl are medium sized.