Is there any historical evidence that is present to defend that any early church leader espoused such a view as described by Dr. RI—either accepted by mainstream leaders or by heresies in its early history. If not, and thus being a modern invention, then I concede that Mormonism exceeds what would be considered my personal limit on what is to be considered Christianity based on the following points; the concept of Exaltation, premortal existence, and on a lesser point the supplementary material synchronizing with the previous points.
The pre-existence of souls was actually a doctrine of Origen, though one that ended up being deemed heretical. It dovetails with a neo-Platonist metaphysics and a whole host of unusual doctrines that found greater emphasis with his later followers. Perhaps the most curious Origenist doctrine is the belief that we will be resurrected into spherical bodies.