As you probably know, NIA does not consider aging a disease, just a risk factor for other diseases. So we cannot possibly test anything remotely risky in humans for the treatment of aging, and that certainly includes both transplants and gene therapy. We have to backdoor our way in via stuff like Alzheimer's, dementia, sarcopenia, etc, and it seems unlikely that most gene therapy interventions that target aging per se would have enough efficacy on that kind of disease to justify the risk. They are too advanced already.
Even so, this is the kind of thing I think about while driving to work, frustrated at the slow pace that occurs while working within the system :)
I am inclined to agree that the problems with transplantation, both biological and mechanical, are mostly solvable though. I think the kinks will have to be worked out in other fields where prosthetics, surgery, and gene therapy have a better perceived risk/reward ratio than aging.