Larger screens and better battery life are givens with an inevitable redesign though I don't think we'll hear about one until next year. With the current design, there isn't much Nintendo can do to make it smaller and lighter besides replace the SD card slot with Micro SD. They might want to do that anyway. Nintendo will probably rearrange the placement of the things like the camera, mic and home/start/select buttons.
More RAM and the second analog stick are real possibilities. I, personally, wouldn't bet on it though.