Re: just missing the bit in the middle
How difficult would it be to handle the portion in the middle?
I'm no expert but I'd say that's by far and away the hardest part. I could see this technique being extended backwards to handle a fetus with just five or even four months of growth, but it basically needs a vein and an artery to work with, which is going to get progressively more difficult the smaller the fetus. Then the problem at the other end is handling embryogenesis, from implantation and gastrulation onwards. I don't know if we even know yet what hormones and growth factors might be necessary to trigger gene expression and cell differentiation correctly, or when to apply them.