I've been mulling over this idea since it was posted, and I've liked it, found it very attractive, but... it just doesn't sit well - like having a burdock in the pants, however I move or wiggle, it's still felt stinging the skin. The 'stinging issue' I'm having with above is that the idea of brain hemispheres appears to put too much focus on physicality.
So, was thinking if there is something in a body (or something of a physical body) that makes a difference vis-a-vis OPs and Souled humans, what would that be? And the answer appears to be conscience, i.e. I don't see anything else in our bodies that could make a difference, except having a conscience. When this perception is paired with hearing that psychopaths, big and small everyday ones, have been called "people without conscience" (and Cs called them broken or malfunctioning OPs) I would hypothesize that an OP is in fact person born without a conscience.
On the other hand, a person born with a conscience is not automatically a souled individual, but has a potential to grow into one when conscience is developed and strong enough to engulf the center of gravity and transmute it into magnetic centre, so not only to attract matter as usual, but also to magnetically bring closer or 'pull down' the higher center(s) to it, i.e. seat the soul into the body, OSIT.
Regarding the 50/50 information, i.e. C's answer about the division, they also said (read it in the Wave recently) that gender determination is also just luck, suggesting 50/50 division in that situation also. However, as you said, we know that M/F birth statistics is not perfect 50/50, and to my knowledge, when it comes to Nature, there is no 'perfect randomness' or 'pure chance' in it. The actual situation usually reflects the 'imperfection' of Life itself, be it a simple 'step towards more balanced situation' (natural accommodation of the surrounding circumstances) or/and a conscious intent that changes otherwise clean, undisturbed and exact mathematical probabilities, i.e. pure chances.
With above in mind, here comes a huge guess, in all of its extreme 'political incorrectness': having a 'conscience seed' is pure luck, there is 50/50 chance (without taking given circumstances into account) that a newborn is born with it or without it. Without it, there is no possibility for a soul to seat in the body, and as it is very difficult (almost impossible) to grow a conscience from nothing, it's also very difficult for an OP to 'grow' a soul. OSIT.
If above holds any value, it might 'add' additional layer of meaning to Cs saying (paraphrasing); Programming is (almost) complete.
As I see it, 'modern' educational system basically since its beginnings in mid 1800s, have been indoctrinating people (everybody) to think of having a conscience. On top of it, with Church's definition of conscience being "Ability to do Good", not only they programmed everybody to think to have a conscience, they also allowed themselves to costly sell the illusion of Heaven/Hell in afterlife since they also made an appearance of holding the definition of Good.
Anyway, this 'programmed' notion of thinking to have a conscience appears to me to be almost completely opposite from truth as I see it; instead of being something to think into existence, real conscience is sensed into being.
If this view of conscience holds a value, it appears to me that it might be an additional clue/info about Knowledge&Being connection in us and how that 'reflects' on level of our soul development. And it also might shed a new color of light on Cs saying; More suffering is needed for more people to awaken; since from personal experience might be said that hard snoringly sleeping and comfortably dreaming conscience surely would need quite a shock (or/and suffering) to wake up.