The main physical/ergonomic changes I'd make to the G1 are:
1) dpad instead of trackball
2) move the data/charging/headphone port to the side (on the side of the chin, near the camera button)
3) make the chin flat (not flush with the keyboard, but non-angled)
4) put a second "chin" at the other end, that is also flat, making the screen slide straight instead of in an arc. The second chin would have the ear speaker and status light on it. I'd also make the screen take up more of the sliding mechanism (less bevel area). Internally, I'd use this extra volume to make room for a larger battery.
5) make it a tilt screen
Other than that, I'd pretty much leave the physical design the same. Maybe add an LED flash for the camera, but that's not really an ergonomic change. I'm agnostic about a 3.5mm headphone jack, but the 2nd chin might provide a place for that.
