Well I don't care about technology used, I don't need multitouch, but I do want pinpoint accuracy. That is, I want to be able to hit a 8x8 pixel button accurately with a stylus or similar if there's the need.

Whether the OS is designed around the poor accuracy of some newer screen or not is irrelevant, I want to run vnc and I want the ability to run software not designed for handheld.

The GNU Linux based system in maemo is pretty ideal. I've never before had a phone that I could sync, transfer files and use so easily. Thanks to being able to run openvpn seamlessly too, this is also the first phone ever I've actually been able to access my email with. It could perhaps also be done on the android phones, but they'd probably need rooting first. Being able to "just do it" on the N900 is a big big big plus.

The seamless use of tools I know from desktop is the biggest feature for me. ssh, vnc, and all the other unix tools transform my phone from a phone into a powerful workstation ready to do most tasks, on the go, in my pocket.

root is very nice because then I can actually setup the phone to be able to access my email, for example...

I like the physical keyboard. The problem with onscreen keyboards in my opinion, is that it steals screen space. Space that could otherwise have been used to display information is taken away. When on a 3.5" screen you can't see the text you're writing a reply to, or indeed even see the start of your own reply easily, the onscreen keyboard fails.

Of course one could have "exotic" solutions like two displays, one slide-out display for keyboard and one display for content.. But I think I prefer hardware keyboard with decent tactile feedback.

The screensize of N900 is definitely too small. N810 was better. Perhaps the ideal is somewhere around 4.5 - 5.5".

As for tablets, I have a 7" tablet. I thought it'd be really cool and convenient, but it turns out to be difficult to hold upright.

As for speakers, if Nokia managed to bring back the awesome speakers of N810, I'd be happy. Also I wish they stopped messing with the sound in software... And I wish the volume went low enough. The lowest volume setting on N900, for example, is not low enough! ;-)
On N8x0 the noise floor is very high. You can even hear it through the default speakers, one tap with stylus and the sound subsystem is activated to make the tap noise, stays active for awhile, making noise. Manufacturers need to also focus on the analog quality of the signal coming to the speakers, and not just on making excellent speakers. The situation is thankfully much improved in N900.

Megapixels is a stupid measurement. After 2 megapixels, they seem to become increasingly counterproductive. I wish they would use a much much bigger sensor size instead, so that the megapixels produced something else besides noise.

About 1000 Euro or so, though if new devices don't significantly improve on my existing N900, I wouldn't bother unless the price is low enough that it wouldn't hurt too much if the new OS turns out to be unusable playskool "my first touchscreen"-type fingerpainting garbage and I end up throwing it in a drawer.

Other requirements:

Decent CPU. It doesn't have to be top of the line as long as it isn't ludicrously underpowered.

RAM, RAM, RAM, and more RAM. Lots of it. Heaploads of it. Shitloads of it. More RAM than you can shake a stick at. RAM that makes people blush and say "Gosh, I don't even have that much in my laptop, maybe I need a new laptop..."

Actually, a tablet the size of a netbook, with touchscreen, and a keyboard that slides out then rotates (kinda like N97) to lock into place and form a netbook-like shape, sounds like a cool thing. Don't know if it'd be actually usable before trying, though...