As time goes by we are going to find an almost un-limited capability provided by stem cells. Research in many ways is in it's infancy in this line of science. An analogy would be where perhaps in the second or third year after TI then shortly after Bell labs created the first transistors. At that time it was beyond the wildest dreams of most researchers as how things would progress over the years into what we now take so much for granted. Same scenario will be found to be the case with stem cell research.
Very early on, one of the problems with stems cells was using a mouse host...and the potential mixing of species.
We know a lot, but we don't know it all. Look at the premature aging of Dolly. They thought they had it perfected.