As with all things in biology, these are latices of compromises that are best viewed in the way of the individual interests at stake here. Father, mother and child. While I don't disagree with the notion of cell exchange, it is after all one of my intro statements, the problem here is that there is a narrow range where it becomes relevant: the range of injury where a cardiovascular shock happens that is significant enough to induce a miscarriage and everything below in severity.
And that is a narrow range in a lot of cases because above it you're more looking into death by sheer trauma, or side effects like cardiac arrest and strokes and below it you're looking into mostly negligible injury that will cause a lot of discomfort but seldom endanger either mother or child, disregarding infection.
Add to that the counterbalance that is the increase uterine bleeding where you get a potential danger to mother
and child and it seems more like your proposed cell exchange bonus in this system is a side effect of a fix to a problem.
Mind you, that is not only the fault of the missing cell layers, but the entire morphology in this case. Because rats mostly solved this with a diffuse haemochorial placenta.
And no, you will not convince me that freely flowing serum is a good thing, because that introduces a host of immunological issues that shape the life of a child forever and, especially in regards to the Rh factor, can actually have a lot of consequences.
In regards to the implantation issue, that is based on the fact that implantation and the time of about two weeks after are a major bottleneck for successful pregnancy and there is a dark number of pregnancies that terminate in that stadium that is, at least by the implements I am aware of, not small. Those usually result in the 'huh, I'm a bit late this month'-scare.
That aside your assertions in regards to regulation of the regeneration are pure conjecture when you have to consider that the sheer heat displacement from some of the major regeneration feats of both Logan and X23 would denature any proteins involved in the process. And that's not even going into the Hayflick limit.
I said 'conservation of energy-defying healing factor' for a reason.
But, admittedly, at that point we're taking the whole discussion ad absurdum because neither physics nor chemistry nor biology matter.
Still it's fun to talk to someone who knows their stuff. If you feel the need to continue this and try to get me off the idea that epitheliochorial placentas work best, especially like those found in some types of shark, I'd love to see you in my DMs instead of clogging the thread.
Fuck Nosgoth though, all my homies hate Nosgoth.
I still miss Tony Jay and the days when Amy Hennig wasn't held back in writing.
At least the few soul reaver memes are good.