This.

This too.

Pokémon.

Kids are also turning their attention to ipads and smartphones. Kids are so spoiled these days....but I truly believe the 3DS will be the last major handheld only machine (well it's not really a handheld only machine, Nintendo is bringing out a movie store and it plays MP3s, but you get my point).

So judging by the OP we are not bound by practicality, feasibility or wide appeal more just make a system for tech heads and gadget freaks like me. 

So for a start it would need a opaque (as in can't be seen through) multi-angle hologram projector capable of projecting a fully realised 3D scene up to at least 1 cubic meter, and capable of projecting a flat screen for personal use and text, video and classic games etc.

The ability to use the cell phone network anywhere in the world to download apps and other media from the store without paying a carrier, sony would pay the cell phone networks a % of all sales.

an 80GB HDD like the ones used in the iPod classic.

a pair of 3D cameras (front & back) for gesture and facial tracking and augmented reality plus 3D home movies.

Fully featured web browser.

and that should about do it...

also who was surprised by the the 3D reveal at E3? The screen was practically confirmed months before.

The support of the industry. However from the looks of it, the 3DS has a lot of that sewn up already.

Personally? No, I haven't had a close personal look at any of the displays listed in that link except the 3GS display.

What probably impressed you was the super-saturated colour. Kind of like this HDR photography, AMOLED's excessively vibrant colours look cool, but they're a negative any time you want the display to accurately reproduce a real-world image, such as when you're taking photos or trying to create realistic graphics.

In terms of picture quality, the only places OLED decisively beats LCD is in contrast and viewing angle (the latter is pretty irrelevant in a handheld). LCD is brighter, sharper, and gives more accurate colour.

Crucially, OLED drinks more power.

They're good displays. If LCD tech didn't keep evolving, AMOLED would be a damn good substitute. I just get frustrated by the excessive hype for a display tech which is a sidegrade at best. And since I place a very high value on battery life, I'm not going to buy an OLED device until its power use gets more competitive.

@Solid_Snake

Sorry for the misunderstanding. You're right that rollable displays are an interesting idea which could help make handhelds more portable.  And that's a good value, since the current generation of handhelds are barely pocketable.

Huh? When have Mario Kart, Starfox, Kid Icarus, Zelda, Animal Crossing, or Nintendogs ever been on a PlayStation platform?

OT: Games of all kinds. Sony hasn't shown me that they understand the handheld market is quite different from the console market. Superior online capabilities would be nice and shouldn't be too hard to imagine happening anyway as well. Lastly, it needs to be affordable.

buy nintendo and release mario exclusively on PSP2 LOL.

That would also make the internetz explode!

gran turismo 5 Portable would be an awesome selling point for this.

Don't forget R&C, Jak and Daxter, An Ape Escape Game, Motorstorm, RIIIIIIIDGE Racer, Killzone, new GTA portable, Crash Bandicoot, Metal Gear and more other sony/3rd party IPS and this PlaystationPhone WILL sell.

Don't forget Monster Hunter Tri Portable too =)