In my opinion this kind of research crosses some ethical lines that shouldn't be crossed. If one considers an embryo as an independent life, what species the embryo belongs to? Wouldn't be the ones in this experiment half humans with human rights? After all, the scientist doesn't know all, and the cells he put in could evolve to a chain reaction of the hybrid developing human conscious.
Just my opinion tho, as I know nothing about genetics and biology.
I think the line of inquiry into replacement organs can be researched ethically but the how of the research may cross ethical lines if not done carefully. Given diseases we have, I think we need to do the research and find an ethical way to make this kind of organ production happen, if we want to extend human lifespan.
About the research, I hope I am wrong and the advances that came out of it help save lives and extend the human life. I just wish they take those ethical questions in consideration too.
When an issue will not be settled no matter how reasonable the first party is the second party is either motivated by tyranny or just principles. The former requires force to suppress. The latter cannot be suppressed forever without destroying the goods the first party wishes to preserve.
Arguments from ignorance are rarely helpful.