I have wondered this myself, I decided that if I did really fancy a classic camera plus digital back, Hasselblad already make one. A secondhand 500cm plus CFV back would be easier, cheaper, more versatile and actually useful. As much as I like the TLR (the first place I worked only used them, we did marine, PR, aerials, studio portraits, weddings etc), the pain of getting it to work with digital would not justify it. Then again I have no desire to climb Mount Everest either.
Kevin.