The problem isn't that it's impossible - the article demonstrates otherwise - but that it's very difficult to pull off aesthetically well. Consider that what you'd want to add, to be comparable to a conventional DSLR, would be the sensor, LCD, image processor, additional controls, card cage(s), battery - it'd all take up extra space, and all on the back of the body, rather than integrated into the overall space of the body.

So, a fairly substantial engineering task, and that's only for a back which would be designed for either a specific model of body, or a small number of identically sized bodies.

Then consider the numbers you'd be likely to sell, versus competing with the units rolling out of Nikon, Canon, et al.

Which is not to deny the geeky appeal of doing it anyway. =:)

Most of the investment in cameras are in the lenses, and I believe you could use your old Nikon lenses on new DSLRs (not sure about other brands), so the pressure was just on upgrading the body, which is relatively inexpensive.

I have been thinking about this for months. It would result in something a bit bulky, but would love to try it on my FM2. In fact, given more time and knowledge I would love to get my hands dirty on this. Main problem: get a hackable full frame 35mm CCD, (or even the full board of a camera) and download raw files to a medium at reasonable speed. That assuming the flash or the bottom output of the camera will sync nicely with the shutter (mostly yes).

Another thing I always wondered is why digital SLRs do not come with CCD "cartridges" and slots. I know that camera bodies are the cheap part of an SLR, but that's the reason I would love this. People would be willing to invest on a good camera body if they were not going to throw it away after 5 years. Things like the Leica M Monochrome would be more of a commodity and less of a luxury.

Ricoh kind of attempted this (albeit mirrorless, not SLR) with the GXR series: http://www.ricoh.com/r_dc/gxr/features.html

If I understand correctly, the body has the grip, LCD, and processor, and you can swap out individual APS-C/lens combo cartridges.