I assume that by adequate inputs you mean things like keyboards and mice. That's easy, either by BT or USB. That leaves adequate outputs. For office use you don't need high frame rates, most common office use is for static images. I would imagine a USB to DVI adapter pretty sufficient for that kind of use. Those five people who need a digital video output may purchase one of those and the rest of us can live with a cheaper Neo with just AV or VGA.

At first glance, SlimPort would appear to be the preferred choice over MHL given that it is licence/royalty-free and also energy efficient. I find it to be a very desirable feature. If you were to include support for SlimPort in the Neo900, how much would you expect it to affect the cost of the final product?

That's completely unclear yet. Depends on us finding datasheets with application notes, a proper reference implementation (other device) that we can "borrow/copy" circuit design from or alternatively how many failing prototypes it needs until our genuine solution works as expected, and of course it depends on the cost for BOM (chips).
If I had to guess, I'd say a maybe 10..40EUR aka 2..8% more, but don't even quote me on this guess please.

/j

Sure it would be sufficient. Care to give a link to the linux drivers? Also, what current do those adapters draw from the USB port?

EDIT:
Oh, and they are not exactly cheap

I couldn't agree more with 'crustacean' about this video discussion.

We are expecting a phone which will cost around 700 euros for the motherboard + 150 euros for the other parts = about 850 euros.

Let's face it: the price is already huge. So do I really care paying 900 euros instead of 850 euros if the 50 extra euros give me the possibility to use the Neo900 as a laptop replacement? Not that much.

Because 850 euros for a smartphone is very high. But 900 euros for a smartphone capable of replacing my laptop suddenly makes it more acceptable.

Please note I used pessimistic hypothesis here.

Using USB as you said is a potential work-around for a single use-case, but it is not a substitute for the large range of functionality that something like SlimPort (or maybe VGA) would add to the device.

Example: My laptop has HDMI output. I have a simple script set up to handle x output and run certain programs when certain events occur. When I plug the laptop into a specific HDTV or a specific monitor, I can have the system boot specific software. When I plug it into my living room TV, the system boots XBMC or another ten-foot UI automatically. When I plug it into my office monitor, the system automatically switches window managers and then boots my favorite productivity software. (etc.) Now apply this same concept to a pocketable, mobile system--the potential is huge.

Also note that I agree with cluxter's above post regarding price. The inclusion of something like SlimPort is a matter of expanding the potential functionality of this device significantly with a presumably relatively minor increase in total cost.

Speaking of laptop replacements, I would think that with HDMI, a similar hack to the Raspberry Pi/Motorola Atrix laptop dock should be quite feasible.

I don't feel the need for such feature as I'm quite skeptish regarding the usability of the device on desktop mode. What about powering the device while the usb port is used to output screen ? Would it be possible ?

Damn .I'm all over this like stink on poo...I agree...TOTALLY...if slim or a comparable is viable in turning the neo into a truly laptop replacement device ... it REALLY REALLY REALLY makes it worth the extra coin...in so many ways. I do hope it is feasible..bloody hell...I had so many good points on this but I'm just too bloody excited about the prospect... I think my brain just dissolved into custard.

Good question.. Ugh...brain...work! Well slim does have the ability to run and charge the connected device...I would love to have a neo slim enabled. Ugh freemangordon beat me to it.