Quick review of Nokia U specifications (overall, pleasantly looking).
> Display: 4-inch capacitive 16:9
Resistive! I would like to use stylus, and capacitive has lower accuracy (source: Wikipedia).
> Power button, camera, zoom and volume button controls
Zoom and volume button controls - separate from each other, please.
And don't forget the lock slider.

> Shape: Monoblock
With QWERTY keyboard, like N900! Let it have four or five rows of buttons, and let buttons be smaller and better suited to typing by the stylus (seriously; when you use keyboard and touchscreen at the same time, it would be comfortable to press keyboard buttons by the stylus).
> Dimensions: 60 x 110 x 6-10mm
It can be two or three or four times thicker. I wouldn't balk at it.
> Extras: Auto lens cover
Not Auto. Manual, please. I don't want malicious software to take photographs anytime it wants to. And I don't want the electromotors of auto lens cover break and leave me without a camera because I cannot open the shutter.

> Material: Aluminium
> Finish: Soft touch
Any material you want.
> Colour: Single colour
Black.
> Durability: Super strength
Yes, and make the screen unbreakable and unscratchable, too.

> Open source operating system with unlimited multitasking.
Yes.
> The DbC OS 1 sports temperature and location sensors so your device constantly monitors your whereabouts and the local conditions.
Location sensor - GPS - we already have in N900 (and in most other devices). Temperature sensor... It wouldn't give correct reading when it is in your pocket, would it?
Let it be. Just allow me to turn sensors off completely if I want to.
> Device-based storage is supported.
Of course, yes, and no cloud.
> The majority of OS functionality responds to touch control.
Yes.

> Support for 802.11 n/b/g wireless standards.
> USB 3 connectivity.
> HDMI connectivity.
Yes, whatever it is.
> Cable charger.
Yes, definitely.
> Dolby Surround Sound.
Let it be. But it would be more important for me to have the whole range of frequencies which can be heard by dogs, cats, dolphins and humans.

> 8-megapixel
12-megapixel, please. You already have cameraphones with such sensors on the market.
Also, it's said that in N900 the lens is considerably smaller than the minimum physical requirement for a true 5MP camera.
http://wiki.maemo.org/N900_camera_sensor
Let not repeat the same mistake again. Use larger lens for higher resolution sensor.
> 4X optical zoom
I wouldn't mind 10X optical zoom. I want to use it as field glass.
For a good optical zoom, I would tolerate several centimeters long lens retractable lens assembly, like on digital cameras.
Whatever optical zoom is made, 4X or 10X, it shouldn't cause any distortion of the image.
> Dual LED and Xenon flash
Let it be. I can choose which of them I use - or use both.
> HD video capture
Correct. Good camera can record high-definition video.
> Instant image capture
"Instant" is subjective. What kind of requirement is it?

> Kinetic power booster
No. It's good for a wristwatch, but it cannot power such a dragon. Better use solar panel USB attachment: the device in the pocket/bag, the solar panel fixed outside on your pocket/bag. And use crank generator to recharge the device on the go.
> Multiple OS support
Yes, of course.
> Surround Sound Speakers
Not necessary... Let it be.
> Upgradable Flash memory
Yes. Though 32 GB seems like enough right now, hardware has the tendency to become better with time.
> Upgradable image sensor
Yes.