NGT, I couldn't agree with you more, with the exception of the battery power but that capacity is not expensive, weighty nor hard to include so I don't see it as a problem. Mainboards run on 12 volts anyway, so its just a matter of bypassing the transformers in the power supply (which I would make external). For an idea of what you are talking about take a look at this: http://www.mini-itx.com/projects/attacheserver/
I realize its not the full monty of what you are asking for but its a long step or three down that road. I've been playing with the idea of an attache-computer for the last year or so. Something about 14" x 19" x 3", about the size of a typical attache case. A finned aluminum case connected via heatpipes to the major heat sources so you don't need the fans. That size will also allow for a 22" wide screen LCD or better yet, an OLED display, takes less energy, produces less heat, provides a much better image (faster, brighter, higher contrast), plus only 1/8" thick. Perhaps make the lid a folded membrane radiator to assist with dissappation of heat, connected to the guts with a heatpipe hinge (http://www.thermacore.com/pdfs/adv_hpt.pdf
). Get rid of the legacy tech ports, providing maybe three or four of the new ExpressCARD slots. Meanwhile, inside, there would be a standard PCI Express BTX mainboard but with right-angle connectors for the slots. With that depth, there'd be enough room for three add-in cards. The video card would be oriented the opposite way, over the CPU with a major heat collector between the CPU and the GPU, connected via heatpipe to the case and lid radiator. If necessary, put some peltier elements on the downside of the heatpipes to assist in dispersal to the radiators. I'd want a built in keyboard, something like on the bigger SAGERs, I use that all the time and its fine. Of course, I'd make it detachable and wireless. And there should be more than enough room on that big deck to include a real touch screen digitizer screen, small but useful. I happen to like touch pads, I'm a touchy-feely kind of guy, but that could be an option with just a mouse pad for you mousey types. That would fold out and/or be detachable as well. Naturally, there would be a series of modular SmartBays, maybe four altogether, on one side or the other (easy to make left and right handed models), those would be 5/8" x 5-1/4" so they'd take just about any standard drive there is. Again, all plug and play, hot swappable. Just a matter of getting the brackets to mount them. On the other side (not the back) would be the I/O ports, that's so you don't have to get up and look back there to plug stuff in. It should be possible to make the add-in cards accessible without taking the thing apart, making them pretty much plug and play as well. On the bottom, there could a connector for a battery plate. Kokam has a 3.7 volt, 70 AH LIon battery that measures 1/4" x 13" x 18". The battery is optional, there would be a small UPS (uninterruptible power supply) inside, maybe 15 minutes worth). That Kokam has a capacity of 250 watt hours, which would give roughly an hour to 90 minutes of run time, depending on your usage. Making those battery plates stackable would give you modular battery time if you wanted it. Two would get you through most any DVD, three would get you through most anything else. Provided, of course, you wanted battery power. You could just go without. Adding that ability would cost less than $20 and a few ounces and there's lots of people that would want it. Plus, being native 12v, running it off your car would be no sweat, provided you have the battery and alternator for it, most current cars do, though you might not want to run the AC and headlights plus your 600 watt sound system at the same time.
Its all doable, all of those parts either exist or will exist within a year. They will all be off the shelf items. Substitute an LCD for the OLED screen, and a current top end PCI-ATX mainboard for the BTX-PCI Express mainboard and a couple of other minor items and you could do it right now, all with off the shelf items excepting the radiators and heatpipe hinges. You'd have to get those made up special but they can be done. Probably want to make your case too though you could modify a photography case. Cost, probably not much different than a new 8790 with the works. Most of the cost would be the components. Time, probably take 20 hours or so to construct it. Figure a couple of hours a night, maybe two weeks. I have a lot of it modeled already in 3D, I'd have been done last summer but I saw the coming changes to PCI Express, BTX, 64 bit, etc, so there was no point in finishing up what would become obsolete before I got it built. I am waiting for the release of PCI BTX mainboards with Socket 939 to get the dimensions of those to model them and finish it up. The Socket 939 is because I'd want to use an Athlon 64 FX processor. 64 bit is going to happen and its going to happen much faster and much bigger than most anybody thinks. Intel is going to suck a lot of wind on this one. I think AMD is finally going to show a profit and the next year its going to be a whopper. Then again, I wouldn't believe anything I say, after all, I've never made a killing in the stock market previously, no reason to believe that's going to change.
Anyway, that's my dos centavos and where I'm going. If things work out, I hope to build it this fall, maybe start on it this summer. Of course, I will post pics. If not, then I'll be buying what I hope will be an Athlon powered SAGER next January.