[dejj]

Yes. Afaik from Nick Lane’s “Oxygen” the Cytochrome Oxidase made from the mitochondrial DNA have to match the Cytochrome C made from nuclear DNA. Even slight mismatch seems to lower mitochondrial performance and is a problem why heteroplasmy (mixing of mitochondria from father and mother) seems to be selected-out.

[treyd]

Well what if you also swapped out those genes?

[dejj]

If your mitochondria have bird DNA and your nucleus has bird DNA, then you’re a bird.

There’s an easier way. A single nucleotide polymorphism (SNP) that only and rarely is observed in Japanese can extend human lifespan greatly. Flip a single base pair. This seems the most promising first step for genetically engineering humans.