I really liked your article, @honeydue. Too bad I can't access, on this side of the earth so mistreated in the last 20 years (Venezuela), writers like Liviu Rebreanu and Marcus Sedgwick, particularly those attractive novels he comments: Adam and Eve and Midwinterblood. As you point out, the idea or image of the reincarnation or transmigration of souls has a curious universal character (one could speak of "archetypal" meaning in Jung's thesis), and, beyond religions, we can find it in different literatures and manifestations of art. I think of an excellent tale by the Argentine writer Julio Cortázar ("La noche boca arriba") or some by Jorge Luis Borges. Also in the cinema there are interesting works, such as Inception by Christopher Nolan, perhaps a very modern version of that idea.
In the image of the "soul mates" I consider that there is also that archetypal Jungian character, and that, in addition to what Plato contributed, we can associate with the idea of symbol, as Hans Georg Gadamer shows us in the etymological revision (Greek origin) that he makes of the term in his book La actualidad de lo bello.
Thank you for your magnificent work, @honeydue, and @adsactly for spreading it. Greetings.