USB Storage with DSLR

I think it would take more than "a few more lines of firmware". A NAS has an entire operating system with dozens of subsystems.

Any programmer or system designer would warn of substantially increasing the complexity of a system just to handle one feature. Because then you've got all the attendant integration, testing and debugging issues. Maybe someone who has done such work knows how complex the code needs to be in this case.

There might be hardware changes needed as well, since the port might have to recognise other protocols.

Bear in mind that plugging in any possible hard drive (with any capacity and any disk formatting) is orders of magnitude more complicated than plugging in a fixed-sized memory card that the camera has the rights to format as it wishes.

Wow, that's bad luck or something! I can see how that would burn you, but as a systematic error it's not likely to happen with a reader you've already tested on non-crucial data. I would hope!

Let us know how that works out.

The issue with these devices, as with blind USB host drives, is that one has no real confirmation that the file copy has worked properly. There is no reassurance a screen would provide and no way to view the destination storage area.

There are more expensive devices with a screen, but they are way more expensive. At that point you may as well take a netbook. Or, my preferred solution, a normal USB HD one can plug into any old computer one may find along the way.

I prefer being very sure my files have copied to being able to copy them quickly. Besides, I would always want a second, off-site copy (say, on DVD) which is going to require a computer anyway.