@Jabberwok:
I found it to be more an unexpected acknowledgement of her personhood. Calling her by her full name implies that she might be more than just a toy to be used for his whims.
On the complete contrary. Her name is Kurotsuchi Nemu, it has nothing to do with "Nemuri Nanagou" so it's not a matter of full name.
"Nemuri Nanagou", as translated by mangastream, means that she is his 7th experiment. So it shouldn't be seen as a "real name", but as a label. It has nothing to do with aknowledging her as a person, but treating her as an experiment. Mayuri used this label to remind her she is not a person on her own, she is his experiment, his property.
Obviously, Kubo is a fan of redemptions, so in 1 or 2 chapters we'll find out that Mayuri actually cares about her and is trying to hind that, but in this chapter he was actually treating her as less than a person and trying his best to make it clear. If he really wanted to aknowledge her, he would call her by her true name "Kurotsuchi Nemu", the name that carries his own surname, that identifies her as his daughter.
EDIT: And about being impossible to recreate her, he, again, said the complete opposite. He actually said that he could make a new her, but it would require a lot of time (and effort). So, as someone said, the reason he gave was that he would have to "level her up an 8th time". Because she is just one more among many other Nemus. Six came before her, others could come after… but if creating another one could be avoided, Mayuri would prefer it.