The issue of mitochodrial transplant which is behind all of this is quite complex. The energy efficiency of the mitochondria will drive splices. Splices are where a gene can produce different proteins dependent on the circumstances.
Hence if you have too efficient mitochondria you will not necessarily get the right proteins. I think getting new mitochondria is a good idea, but it needs to be done carefully if from external sources. Internally the body shares around mitochondria as a response to things like exercise. I think the HIF 1 alpha transcription factor drives a lot of mitochondrial sharing.
What Rapamycin should do is improve the average mitochondrial quality in any one cell (depending upon dosing). There is, however, a limit on mitophagy in that
a) Mitochondria in a cell can only be averaged up to best mitochondria in that cell.
b) Some damage to mtDNA can damage the mitochondrial effectiveness without reducing MMP and MMP is used to identify flawed mitochondria. Mutations to ATP Synthase fall into this category.
However, my view is that a lot can be done to improve energy levels and cytosolic acetyl-CoA levels as well as directly impacting on transcription levels. These use the body’s own systems and are, therefore, unlikely to be harmful per se. There do remain, of course, the issues about side effects such as Rapamycing reducing stem cell production.
My point about mitochondrial transplant is that it can in some circumstances be harmful.
I also think that longer lived species have better mechanisms for maintaining mitochondrial quality. Ignoring all the issues about the practicalities of taking pig blood to generate transplantable mitochondria there is the big issue as to whether the mitochondria are in fact ones you would wish in preference to your own mitochondria much that there would be a mix.
Xenomitochondrial transplant is probably more practical than most xenotransplants, but I have not read up on it and it would not be my first preference.
Mitrix Bio’s approach is I think quite interesting in that they take mitochondria from an individual and aim to grow more mitochondria from that and then return them to that individual.
There is actually a question even from human mitochondria as to compatability of mtDNA with nuclear DNA.