You make some fair points.
Except for the psychological strain of learning the facts around ones existence, being a scientific experiment, the only one of your species in existence, etc.,
Certainly the experiment angle would be important. The kid's life would be a bit too Truman Show...
I'm more concerned with the physical aspects. In 50k years our species has evolved physiology to deal with this environment. Imagine going back 50k years and asking your physiology to deal with all the foreign bugs and parasites it's never seen before. Or 50k years from now.
That would be a concern, but how much of our disease resistance is genetic? Wouldn't it gain some resistance from the mother during pregnancy?
We do not know what 50k years of physiological evolution has done. And I can't get over the fact that this experiment is being considered on a sentient human being.
I agree. Just to be clear, I regard this as a thought experiment only. Apart from anything else, I don't really see what is to be gained from actually doing it. I'm sure sure what it would really tell us about the original Neanderthals, if anything. No, as you say, the unknowns are too great. It is interesting to consider though.
Mutate and Survive