Actually, looking it up my memory is correct. Immunity from actually having chickenpox is acknowledged to last much longer than from the vaccine, and will be lifelong in most cases, particularly if you are occasionally re-exposed to chickenpox (for example, by being around a child that has it). The duration for the vaccine is thought to be about 20 years.
A quick check confirms that the Varicella vaccine is a live, weak virus one
I'm pretty sure I could get the study proposal through the ethics board, there's nothing unethical here and it's an important enough question. I just doubt anybody will consent to being deliberately given a virus that inserts itself into their genome, just to see if their immune system still will recognize the virus and produce antibodies to it.
Based on the two quotes above, I'd say they were already given a virus that inserts itself into their genome albeit a weakened one. It would be their parents who consented (without really being informed). As for the thus far unasked question, can the vaccine strain cause shingles later in life and how does the risk differ from the wild strain, we have no way of knowing yet.
As for the flu, yes it probably would be more effective for people around the most vulnerable to get the shot. I think that so far, a more generalized flu vaccine has eluded us, thus the annual shots.