Being able to dual boot PPC (or even Palm) and Linux would increase productivity quite a bit. Why do you think it would prevent anyone from using it productively?
The fact of the matter is, PPC/Palm are supported in the US, sync on Macs, and have better stock PIMs and some other applications. If we could go back to the days of WinCE2 where you could load a CF card in with Linux and run a boot loader, that would be great. Then I could use PPC/Palm for my day to day business needs and then pop in a CF card with Linux when I need/want to hack. It'd be even better if they'd give us a fat flash chip to load both OSes on comfortably.
Booting takes time, whether from RAM or cf, doesn't matter that much. If you want to use the Z as a PIM device, this would be too much time. Imagine situations like this: "oh, hang on just 2 minutes, I'll have to look up this telephone number/ckeck my schedule" just because you were hacking the shell and need to reboot the device.
It's form factor, "allways there and ready and instant on" is was makes the Zaurus a PDA. My laptop needs 3 secs to wake up from sleeping mode, my Z just 1. For me, that matters.