Well, the problem with transplants is that any transplant (not using self-donated or cloned tissue) requires lifelong use of some very unpleasant anti-rejection drugs which compromise the immune system, can impair other body functions, and have other nasty side effects. Doctors are, and will be for the foreseeable future, very reluctant to do transplants of any organ unless its absence/malfunction is a serious physical threat to the patient's life and can't be compensated for by drugs or hormone replacement. Hearts, lungs, kidneys, livers, etc - organs that play a direct role in the body's metabolic processes - are worth transplanting, but thyroids, reproductive organs, and the like - organs whose primary life-sustaining function is to produce hormones or chemicals to support other organ function - are usually not.
(and just from a psychological point of view, I personally would have a very hard time using someone else's genitals...especially if they were producing that person's sperm...kind of creeps me out, actually, even more than what I've got)
I think the best potential new advance for trans people is the developing capability of bioengineering to grow/manufacture organs from a patient's own cells. Even a limited form of this - manufacturing erectile tissue for trans men, or mucosal tissue for trans women, even if they couldn't grow a complete penis or vagina - would dramatically improve current surgical options and reduce the trauma of self-transplantation.