10 years, more like 5 years and we feel like replacing, but this idea would only work on near pro cameras, I think the cost of the sensor module would be to high for the implementation in D40/60/3000 size cameras. You are not swapping shutter/mirror just the sensor assemply, so DX stays DX and who would downgrade FX to DX.
It's not likely I'd upgrade within 5 years if I ever got my hands on a D700. The price would be too high for me. 10 years sounds just about right for me, but of course it'd be different for everyone.
I don't think I'd be interested in that. I mean think about it: Would you want a car with an interchangeable engine? How about your computer (which is interchangeable). How many of us have actually upgraded the processor on a computer? I have... back in the 80's\early 90's (upgraded my 286 PC\AT to a 386 chip. Its never made much sense ever since.
By definition, you are going to have a substantially less weather resistant, and more prone to damage from being knocked around. I certainly wouldn't ever change sensor out in the field. Sometime I carry around two bodies just so I don't have to be bothered to change lenses. I'd rather have mutiple cameras rather than a multi purpose camera (B&W, IR, etc.)
So The question then becomes Would I be interested in an upgradeable camera? I guess i would, but I'm skeptical that I would see much in terms of savings. Ironoically, what intrigues me most about this possibility is the ability to use one sensor with several different form factors of camera (small D40 size for travel, all the way to D3 size for studio \ tripod work).
Not necessarily- the film back door for film SLR's is pretty large. I haven't handled a pro film SLR, but I would imagine that the weather sealing was still enough to handle a brief downpour in a F6 or F5.
The thing that I hate the most is that you're camera will always be outmoded. How cool would it be to own a D2x, drop a FX sensor in and be running with the D3s, while at the same time swapping out the LCD and perhaps the viewfinder as well?
(Assuming everything fits, DX to FX is absolutely possible, etc.)
It wasn't really thought about film- the film always needed to be loaded, but we really can't load new sensors, right?