I think the next device needs to be 'polished' (not in the literal sense). By this, I mean that there should be more attention to detail in terms of feature completeness and useability corner cases.

The next device should continue along the pocket computer theme. It should stay true to its heritage, and continue to fully support easy porting of upstream packages by not focusing too hard on QT and 'mobile apps'.

Finally, and I may be going out on a limb here, I think it could get a little bigger in order to provide a little more battery capacity, a slightly bigger screen, and the 4 row keyboard mentioned above. Oh yeah, proper, USB OTG, maybe with the old style charger socket in addition to the microUSB, so it could power external devices. And a compass.

That would do for me, I think.