I just saw (Tuesday) the above video and I wholly agree with the premise of being transgendered as a result of reincarnation (or should I say, of reincarnation gone wrong).
Scientists just love to talk about fetal hormones playing a part in brain development as well as physical anatomy, and that when the two don't match, the result is someone who is transgendered.
But there's something more important going on here. When you select a new body, you are generally choosing among a group of bodies that are already nearly fully developed. It's like buying a car at a car lot -- the cars are already built; it mainly comes down to a matter of choosing which one you like.
I don't know exactly when the assumption (entering and claiming a body) is supposed to take place, but I remember I picked up this one a day before it was born.
Getting back to the transgendered -- it's mainly a thing where the thetan wants a body of one gender but gets stuck with the other model. I know of two (ex-)Scientologists, both heavily into Scientology and the Sea Org, who were a happily married man and woman in an earlier life, but were two men in this one. The one who was the wife was transgendered, no doubt in a (subconcious?) urge to get back to the happiness that was that earlier life. They are both now deceased, but anyone would recognize their names.
One way of resolving this dilemma would be to have a gay relationship -- but the one who was the husband was an old-fashioned, 1950's-style homophobe, making that impossible. Another method that people have used is for one of them to marry the other guy's sister, so they would be family and have a excuse to pal around with each other.