Cells are swapping their mitochondria. What does this mean for our health?

This could be a mechanism for future intracellular repair. Build little repair robots that look like mitochondria, have them insert into cells, do their magic, then leave.

"do their magic" seems like it's hiding a lot of complexity.

Very much so.

It would be much easier to package those into extracellular vesicles (exosomes or microvesicles) than into mitochondrial-like vehicles.

That has been an active area of research for a fairly long time (decades), and there are already clinical applications that have been commercialized (eg.: mRNA vaccines packaged in lipid particles).

Or you could occasionally fast for 5-7 days to dramatically ramp up the intensity of autophagy/mitophagy in order to have your body do this for you. No robots needed. You may also discover that you like the way your brain and body operate with a different ketone/glucose energy balance.

Any significant amount of fasting is a quick way to get some very unpleasant headaches for me. No thank you.

Low blood sugar and dehydration can lead to all kinds of unpleasant side effects. When I tried to fast for the first time, I was an idiot and didn't supplement with water or electrolytes and I suffered crippling cramps.

Low magnesium? I was having serious muscle cramps and found Mg supplements were highly effective.

Not trying to persuade you to try again, but if you ever desire to, electrolyte deficiency (particularly potassium) is a common reason that people experience headaches or cramps when fasting or starting ketogenic diets. Watch out for sugar in commercial electrolyte tablets though!