For now it seems you would need a donor body to act as the "scaffolding" for your progenitor cells. Pessimistically, there may one day be a blackmarket for scaffolding cadavers with desirable features.

> While the progenitor cells needed to regenerate all of the tissues that make up a limb could be provided by the potential recipient, what has been missing is the matrix or scaffold on which cells could grow into the appropriate tissues.

> ... living cells are stripped from a donor organ with a detergent solution and the remaining matrix is then repopulated with progenitor cells appropriate to the specific organ.

I wonder if a person could also "upgrade" their body, or invent articulate organs with unique functions, such as printing a scaffolding for wings or a specialized muscle structure attached to the hip for opening beer bottles.

Perhaps they can strip back your own body to a scaffolding and regenerate the tissue. You spend a week as a brain-in-a-vat while your body gets regenerated then you start again.

Sci Fi gold.

And by far not an uncommon trope.

How long before the black market would be obsolete (enough data to scaffold any desired feature), though? Doesn't seem so bad.

There's more than just fabrication to consider. The reason they think generated limbs might be useful is that in current hand transplants, pre-existing limb nerves grow into the new hand, giving it sensation. This does not happen with the spinal cord (and anything that made it happen would be a huge therapeutic breakthrough all on its own). The cranial nerves (those going directly from the brain to the heart, gut, ears, nose, etc) are another potential stumbling block.

That said, it does make the (numerous!) science fiction novels that have had something like this as a premise seem somewhat more plausible...