I was just reading through this post. I think that another linux PDA that is effectively like a YOPY or Zaurus wouldn't be that compelling to the mainstream. I personally would like another Nokia Internet PAd or Simpad SL4 like device. These are the specs I would go for:
Dimensions: 7.1 x 10.4 x 1.1 in (180 x 263 x 28 mm)
Weight: 2.2 lbs (1 kg)
Processor: 600 MHz Intel XScale or 800MHz Transmeta Crusoe
Operating System: Qtopia
Memory :256 MB RAM and 64 MB Flash
Display :8.4 inch TFT 800 x 600 dpi - 32-bit color
Input/Output :Touch screen
:1 x USB Host
:Integrated Bluetooth (optional)
:2 x PCMCIA Type II card slot (full CArdBus)- must have
:1 stereo + mic jack
:Microphone
:Speaker
Drivers for PCMCIA wireless LAN cards (choose 3 types)
Battery: Lithium Ion batteries Up to 7 hrs per charge
The challenging thing would be the price!
You would have to do it for $200 to $400 USD
I would definitely buy it!