Firstly, some people seem to think that having a better spec than what the Z has for a similar price is not possible. That is plain wrong (Unless the great screens shifts the price up significantly). Many devices around the price of the C860 / C1000 have bluetooth, wifi, CF + SD + Mic, and some have a camera too. (Look at Fujutsu, Dell, HP high end PDA's)
As someone said earlier, mixing a C3000 & Dell X50v would pretty much do the job. (Basically, X50v, without graphics processor, with keyboard, better screen and Linux). If it was produced on a big enough scale, it should cost just a little more than an X50v - I'd say very reasonable for such a device.
I think the ideas handheld-linux has put forward are decent. I'm interested in the mini-laptop type PDA, and the spec seems good. It is still very true that such a product would not be a great success unless there is fair investment in the software. The products will need to be good for the masses, not just us enthusiasts, which I think they can be - there are no other good clamshell PDA's out there.