I would assume that like a lot of regenerative tradeoffs, without sufficient global state, just producing more organelles without limit would be a cancer cell's dream.

Given that we only published confirmed evidence that mitochondria sometimes decide to ditch a cell and run around on their own this year, I would be willing to bet decently heavily that A) we're going to find research about cancerous mitochondria being a metastasizing vector in the next few years, and B) a bunch of data on what makes different mitochondria more or less effective over time.

My personal guess would be that, like a lot of senescence problems, it's an accumulation issue - if a bunch of regeneration mechanisms are based around donating mitochondria, then after you hit adulthood and stop printing new cells like you're zimbabwe's currency, it starts having much more noticable of a permanent impact if cells do that, since there's less new ones being created passively...leading also to more need for them since you need to repair more things versus it just being washed away in the constant replacement, and a spiral ensues.

But that's just wild speculation. I suppose a data point in favor of that would be if all-cause mortality is statistically significantly up the more body mass you have permanently removed (e.g. missing limbs), even controlling for exposure to risky things.

It might also be interesting to see if this kind of infusion at a large scale significantly can impact your body's "learned" fat retention, since it's known that, like how an athlete who has fallen out of shape can get back to a level they formerly trained to much more readily than someone training anew, so too does the body "learn" to start retaining things as fat more and not really unlearn it, and afaik we don't know the mechanisms for that.