The amazing part here is that the immune system is very much involved in the early parts of the pregnancy. Successful "implantation" of an embryo in a transplanted womb with an immune-suppressed host is no mean feat...
I don't understand why the successful implantation of the embryo is amazing.
Many women take immunossupressants while pregnant, and many undergo IVF to give birth, some of which to allogeneic embryos (egg donations). This last one doesn't seem to affect significantly implantation, with the main concern being a higher risk of pregnancy hypertension[1]. I expect conceiving with an allogeneic uterus would be similar, since in both the genetic differences between embryo and uterus are comparable.
Succeeding in combining the two is just a matter of probability, which I don't think is that low. Especially if you consider that the uterus had to come from a compatible donor, so the number of HLA mismatches will be lower.
