It's not replacing your screen that's the issue - if you're replacing one screen with another, exactly the same model of, screen, you're set.

But in order to set up an electrotactile resistive screen where just a resistive screen was before, you'll have to do some hardware rewiring. If you're lucky, it'll just be some wire soldering. If you're unlucky, the hardware on the N900's motherboard will need an entire new BUS attached just to be able to communicate with the electrotactile layer of the new screen.

- Edit -

Let's also be clear on the differences here - one, if people are replacing touch screens on their N900s, they are presumably getting either the same exact screen that comes with the N900, or something extremely compatible, and physically similar. Either way, it is already mass produced. Which means cheap, widely available, it doesn't cost Nokia any extra money, nor do they offer screens themselves as far as I know.. you find the screen to use yourself.

Even with the above, I'm sure that it is humanly possible that some people would eventually make it work. With difficulty, perhaps breaking multiple N900s along the way, but they'd make it happen.

HOWEVER, I was talking about a very distinct idea: Nokia providing the hardware for N900 do-it-yourself-ers. For Nokia to provide do-it-yourself kits, they would have to ONE, design the requisite hardware, two, make it at least conceivably doable without having your motherboard manufacturing equipment, and then actually dedicate plant time, work hours, and so on, to put out these screens. Then they have to ship them to those who order them.

And by the time that's done, how many N900 owners will be around who actually want to risk their N900 by taking it apart, and soldering completely new hardware pieces into the screen (and possibly the motherboard and other parts), all for a feature for which support would still have to be written? I mean, Nokia might, or the universities they collaborate with might, release kernel-level support for these things. Either as a binary blob, or, (cue holy music) open sourced code (end holy music). But then Hildon, and every UI interface on every app, still has to be adapted to actually USE the new electrotactile feature.

By then Nokia and every other phone maker will be a few phone generations ahead, and you'll have at best a few hundred (probably not even in the three digits) N900 users who'll pay the money that it would cost them to even make those kits.

I'm not saying it's not the ideally right thing to do (though by the time all of those conditions are met, you'll be better off buying a phone that has such support already), but I AM saying that it is extremely unrealistic to expect Nokia to release do-it-yourself N900 hardware mods. The Large Hadron Collider is more likely to make a black hole that actually succeeds in growing large enough to suck in the Earth [disclaimer]I am exaggerating for emphasis and comedic effect - I do not actually think it's that inconceivably unlikely - but it is damn unlikely.[/disclaimer].