I think:
- A bump in speed.
- Possibly dual core?
- A bump in capacity and certainly memory.
- A front-facing Facetime camera.
- Keep the same resolution, but support the full retina app resolution at full screen.
- A much improved file transfer function in iTunes, and the ability to move files between apps instead of just making a copy. Maybe a general documents storage area?
- ...and just because Apple likes to always surprise us: maybe some type of low-power sunlight readable mode similar to e-ink without sacrificing the default screen quality.