I'm betting, honestly, on pxa 270 for the next 2 years followed by an incremental upgrade at best, and the end of zaurus. Look at the 3100 & 3200...not even a RAM UPGRADE?!! This is why I'm so interested in things like pocket penguin and neo1973. I think the next embedded linux handheld to do zaurus like duty will not be from sharp--minor Z upgrades aside.
Even if sharp does get kind of a clue and upgrades the hardware (don't get me wrong, I love my 3100 & my 6k) it seems to me that they've been outdone and will stay that way by both FIC and Nokia. The future of linux embedded seems to me to be commercial devices built with the expectation of an open distro