I am too conservative for a multiboot. I would rather have one operating system, and tweak it, until it works-for-me. Right now, Fremantle is the best.
Yes, stylus is a must. Though I would prefer the screen to be scratch-resistant (akin to wrist-watch) and more sensitive to pressure. Contradiction, isn't it?
Screen is fine as it is. Though, I would not be opposed if it was high-resolution, like retina. But then, I would prefer to somehow have two screens: one low-resolution, monochromatic, for the graphical user interface; and another high-resolution, high-color-depth for photographs, camera, movie recording, editing and watching, drawing. This way, you can check time, send SMS, make calls without using as much electricity. I know, I am a grumbler, but if you have to spend a week with your phone without running out of charge, such an option would be handy.
Processor: fine as it is. RAM: 2GB, not more. Storage: 32 GB+option to expand it.
Form factor: preferably slider, but it has to withstand mountain hiking, sea sand, sharp stones, lake water. Overall, it must be more difficult to squash than a brick. Yes, I am paranoid. And extremely attached.
Additions:
magnetometer (compass, and metal finder - if you lost a needle or a tiny screw),
radio transceiver (FM radio, Bluetooth, analog television [imagine how handy it would be in these times, when a lot of people have old analog TV sets, and many TV channels have switched to digital broadcasting; just TV-broadcast a movie from your phone, and you can watch it on any analog-TV display within ten meters]; accepting external antenna for either transmitting or receiving),
TV-out cable (just in case you wish to show your photographs to many people at once),
barometer (weather, or geographical height above the sea level),
Wi-Fi (all its many variations),
microphone with noise-cancelling ability (I am quite tired of observing people yelling into their mobile phones),
speakers and microphone which allow constructing echo-hologram (even if it requires about a minute of CPU-intensive number crunching),
palm-sized paper printer (handy for visiting cards and QR codes)...
[Edit]Camera. Must not forget camera. With flash (maybe, ring of light around the camera). Maybe, capable of moving around, for better panoramas. Maybe, capable of cancelling out the movements of the vehicle. Maybe, higher resolution.
And notification LED.
And both camera and screen must have dynamic range close to than of a human eye, probably slightly higher; about 13-14. Then you will not have to capture multiple standard photographs to get an HDR photograph.[/Edit]
Best wishes.
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Per aspera ad astra...