Upload & Sell: Off
You know, it's really too bad Canon, Nikon, et al., aren't very interested in providing customization options. It should be extraordinarily simple to design a body with user-upgradable flash memory for the buffer. Similarly, it would be terrific to have a user-swappable memory card module so I could use dual CF cards in my D800 and D4, instead of the brain-dead options they gave me. But I digress.
Actually, customization on fairly small consumer electronics like this is pretty complex. There are a whole lot of factors to consider. Just to name a few: swappable modules inevitably increase the size overall item; it's much more expensive to build, especially when you consider that it reduces the bulk ordering options that the manufacturer has (e.g. they can't order ten million of one size buffer memory chips); it vastly complicates the stocking and inventorying with additional saleable part numbers (again, increasing cost); it substantially complicates the testing process since they have potentially dozens of configurations to test (again, increasing cost); it adds additional points of failure.
It's not impossible, of course, but unless you've held a job in the electronics manufacturing industry and seen how the supply chain works, how the test teams build requirements and test cases, how the design teams iterate, it's hard to appreciate just how much goes into making something customizable.
Computers are a little easier in this realm because you have agreed-upon standards to build to, but even there: look what happens when you try to shrink things. Apple and the Ultrabook manufacturers are soldering parts to motherboards, using non-standard connectors, even having fixed configurations of otherwise-changeable parts, like memory, so they can pack electronics into a tight space.
I just think customization would increase cost so much as to not be worth it.