As far as Rachel getting pregnant. I really had a hard time grasping this idea, simply because I really wasn't sure that a Replicant was something purely biological. If it was 100% biological, then I can understand it. In the context of this movie, Tyrell's desire for perfection could have driven him to create a 100% synthetic human with a 100% engineered genome that was patented and created in a lab. Patenting this genome and DNA could have given them the rights to claim ownership of the entity, and therefore consider them a product and less of an entity. What gave the Tyrell corporation the right to create a fully biological self aware entity and make it property? The 4yr lifespan was a way to prevent them from developing empathatic abilities (and, therefore, immunity to the test) to see if they were actually human. Allowing them to live past a 4yr lifespan is what probably caused them to develop enough experiences that they started to exhibit emotional responses and start to actually question their own self worth and sense of individuality.
Creating a "self replicating" Replicant would be an amazing feat of engineering, and if Tyrell could do it, it would actually elevate him to a God like status. Certainly a lofty goal, something I could see him trying to achieve. It would enable him to create replicants without the need to engineer them and grow them in a factory. Imagine trying to build a facility off world, it would take a lot of resources, and that what Wallace was telling Deckard, he couldn't grow enough in his factories to meet demand. If the human race was colonizing planets, and there was a need for replicant slave labor, having self replicating replicant slaves would solve the problem, no need to build factories, the womb is now the factory.
This then raises another question, if they rely on the idea that their DNA and genome are a "product" and patented, and that makes them a product and therefore a slave, what happens to a child born of this union? Are they born with serial numbers, probably not, is their genome predetermined, probably not, it's left to a certain amount of chance unless its in vetro, and the genetic makeup is determined artificially. So, if a child is born that wasn't "patented" engineered in a lab, grown in a facility, has "parents" and has it's own unique genetic makeup , how does that child differ form a human? Can it be considered a "product" and subject to slavery? That could be a basis for a war. You have an entity or replicant that is in all intents and purposes indistinguishable from a human, able to reproduce and give birth to living offspring. What makes them different from a human? They were grown in a facility, but what about their children? Was this the deciding factor that differentiates them from actual humans and allows them to be considered property, that they were grown and not born? So if that is the deciding factor, that a Replicant is engineered and grown, and now they can reproduce, and their child is born, would the child be a product and subject to slavery, or would it be considered human and free. It seemed to me that Wallace was hinting to Deckard that "Off world" has different laws. Perhaps to gain access to an off world colony, you can enter into an endentured servitude to pay your way to a new world.
