What would a sub-notebook Mac look like?

Last week Mac rumor sites reported that Apple may be adding a sub-notebook to its portable lineup. If true, this would be Apple's first step into the sub-notebook market in a decade. Exactly what a new Apple sub-notebook would feature (or even what it would be called - MacBook Lite maybe?) are open to speculation. However, Apple's past ultra-portable products might offer some clues. Apple's first sub-notebooks were the PowerBook Duo line. The Duos were interesting conceptually because they weren't designed as a desktop replacement (like most laptops, including the MacBook and MacBook Pro). Rather, the Duo was designed with only the absolutely needed hardware built in to make it very small and light. To gain full computing functionality, the Duo was inserted into a dock that effectively turned it into a full desktop computer or to a mini-dock that offered access to additional ports or devices. Without a dock, each Duo had only a single built-in port (a serial port that could be used for connecting to a printer, modem, or AppleTalk network) and an optional modem beyond the dock connector. There was not even a floppy drive and a dock was required if the Duo suffered any problem that kept it from booting off its internal hard drive. The PowerBook 2400c was the only non-Duo sub-notebook Mac that Apple ever sold. Like the Duo, the 2400c was kept slim by shipping without a built-in floppy drive or optical drive. Unlike the Duos, however, the 2400c shipped with several standard ports, include a PCMCIA card slot. Although not a Mac, Apple also sold the eMate300 - a light portable designed for the education market that was designed to be sturdy and ran the same operating system as Apple's Newton PDA line. Unlike the rest of the Newton line, the eMate sported a full keyboard and a clam-shell enclosure similar to any other laptop (although with a design similar to that of the original iBooks, which conceptually replaced it). Putting all of this history together, one can speculate that a new Apple sub-notebook will be stripped down to offer a small lightweight form factor. With rumors floating around that Apple has been investigating LED backlighting and NAND flash RAM as a boot disk for portables, it's likely that a sub-notebook would include both technologies as a way to not only slim down the device but also to dramatically increase battery life. Chances are good that based on these technologies, it would eschew a full complement of hardware and ship without an optical drive and perhaps even without wired networking. Apple might even go so far as to remove USB and/or Firewire and focus the device completely on wireless connectivity using Bluetooth. If Apple does rely on flash-based disk technologies, it might go so far as to ship a sub-notebook with a stripped down version of Mac OS X. This where the concept behind the eMate - a blurring of the line between PDA and portable Mac could be revived in that Apple could ship the device using the same version of Mac OS X being used in the iPhone. This would also expand on the Duo concept of the sub-notebook as a device that isn't complete but could be synced iPod-like with another Mac.