I think the biggest issue so far, has been that of the keyboard. Feel free to disagree.
Everyone and their grandmother has had their own idea of what they want from this. I've been after a keyboard similar to a Universal or Clamshell Zaurus, some have wanted chorded keyboards, some folding belkin-style keyboards, some just want a slate.
How about just MAKING a slate, without a keyboard. I propose that a separate keyboard is produced, however the heck anyone wants it, that connects to a port on the bottom of the device. You can have it on a cable, folding, with a Zaurus-style hinge on it so that it folds over the slate part. Whatever. You could either use a USB/M-USB connector, or attach it to the internal keyboard pins, (As long as they're capable of hotplugging.) What you'd end up with is a thicker display unit, and a thinner keyboard that you could flip out. You could carry a blooming Sun Type 6 130 odd key USB model instead, if you felt like it.
In fact, put the ATA connector on the same port and put the hard disk in the keyboard. That'll bulk up the keyboard a it, slim down the base unit, and let you decide again whether you want a 2.5GB notebook drive (With an external PSU or LARGE extra battery) a 1.8" CF-type Microdrive, a 60GB iPod drive, or a 256MB Flash card. Whatever floats your boat.