In order of importance:
- higher DPI.
- faster processor.
- larger screen.
- improved margin/line spacing options.
- better support for PDF (the current support is absolutely pathetic).
- support for ePub (probably not gonna happen...).
- support for CBR/CBZ formats.
- up to 16 GB storage (to accommodate for the above formats).
- better image viewer.
- wireless charging and comes with a Bluetooth adapter for transferring files, making it completely air-tight/waterproof. Or, instead of wireless charging, they could implement solar cells
into the screen (or at least on the back, on the opposite top margin, etc), and never have to charge the device again!