Not much. I would make it maybe 1/4 the weight and 1/4 the cost, but that'll take another few years. An iPad is nice, about five of them scattered around the house is better. (Ever see Star Trek? They have so many fucking PADDs around they'll just hand you one because they want you to read a single one page report.)

I would implement "multitasking" but the UI would still work the same: "closing" an app would just sleep the process and swap the memory out. I would allow some processes to spawn "background services" to play audio and maybe a couple other things.

They would be fully self-hosting machines with no dependence on a PC. Their data would sync to some type of cloud storage in some optimized semi-lazy way. For instance, if you download a recipe book on your bedroom iPad upon waking up, it'll show up on your kitchen iPad by the time you get to the kitchen. (If it's not actually loaded, opening it up will transfer it over, possibly p2p from the other iPad.)

And of course, it would have infinite RAM, storage, bandwidth, and CPU.

   1. A bit more ram.
   2. A camera
   3. Lower price.
   4. Time to mature.

Without too seriously violating the design goals of the iPad: add a camera.

But without that constraint, I'd make it run a full OS (my preference would be Windows 7, but OS X would work for those who like it, I guess), with some kind of clever gesture layer of course.

Make it foldable in half. Advantages, it fits into a blazer pocket and makes carrying it much easier. And can also protect the screen. Here's for foldable displays.

Multitasking with an elegant interface (which is a given for Apple). Also, maybe a little lighter. It's tiring to hold it up for long periods of time.