If we are in fact able to bring back the recently-sequenced woolly mammoth, and if we are in fact able to fully sequence the neandertal genome, should we take the next logical step, and just what would that imply?
Personally I think the two "ifs" are a lot bigger than the article's author seems to think. Still, it is an interesting ethical question. In my opinion, one of the many arguments against slavery is that it wastes the potential of someone who is in a very real sense no different than anyone else. Suddenly, at least on paper, we are rapidly acquiring the ability to create manifestly less capable beings, which are however still related to us.
To put it another way, we don't turn chimps into slaves because they're high strung, not that clever, and can bend cold steel with their bare hands. If we are able to create a much more capable, pliable, and less dangerous hominid, what would that imply about the morality of slavery?