Yes, sleves
Imagine a one size fits all PPC, you buy a medium size/spec cheap PPC, and adds what ever extras you want/need, like USB Host, FM radio, TV tuner, (S)ATA plug, camera, multi card reader, you name it. Wouldn't that be nice?
Ofcource the more you have build in, the better, but since no two persons have the same needs, you can have one, that meets the most of them, and add on what ever needs, the future might bring, and still have a normal size PPC, which actually fits into a shirt pocket (Which my 210 does not).
The last sleve/backpack I bought, was for my HTC Himalaya, it had CF slot, VGA-Out and a build in 750mAh additional battery, to compensate for the power use, during the slideshow pressentation, and I loved it. No need to carry a bulky heavy machine, just plug on the extra functions when needed, and drop them back in the briefcase, when done, no Laptop needed
A backpack could also be a docking station, like the ones for Laptops, turning your PPC into your PC, with a 19" screen, full size keyboard, mouse, and LAN connected, just place the PPC in the slot, and you are up and running