Gman, nice to hear the feedback about your nephew. Riding position might be a concern, only way to know any of this is IF the day ever came, try riding some of the bikes first. Believe it or not, I never, ever rode any of the bikes or bike models I purchased but with the Concours it would be a valid point because if there is a concern that would be it, as I have sat on them in the showroom.
Honestly gman I dont see how any bike can have as smooth airflow at 70 to 90 MPH then my Road King, its truly effortless. So that is not even on the list for reasons to want to try a new bike, truly cant ask for anymore more from the Road King except maybe want a new experience. I can literally take my hands off the handle bars at that speed with cruise control on. I dont but I can.
No matter what bike, helmet, height of the rider and passenger, riding style will affect airflow but will be more standard among fairings, for better or worse though.
My RK is set up perfect with a custom height windshield for both my wife and I, HD Fork lowers (fangs) makes it perfect. I suspect you son is not set up like me, whether or now he has lowers, though I suspect he doesnt and is a must on any interstate cruiser (for most) I never owned a cruiser without installing them, which makes 3.
Nothing against the HD fairings, wouldnt mind one, even though for me its not as much a "thing" but the price matters to me now more then back in 2014 when riding was a primary recreation and now sort of takes second place to my wifes boat. Even then I choose the Road King because I liked it best, price made no difference and were very close BTW between the RK and Streetglide..
*L* I tried to check out an ElectraGlide standard, they are nowhere to be found this year and not sure it would appeal to me, as they REALLY went out of their way to strip it down. *LOL**
With that said, one concern to me would be how airflow is but biggest thing of all is price now, touring Streetglides are $10,000 more then the Concours and again in my down sized life, I wouldnt mind shedding the extra 100LBS+ of a Harley. I honestly dont even know how much longer I will be riding though I cant imagine not ever riding, love it.
So I guess you could say, I see the Concours as a way to experience a new bike at $10,000 less then a Harley Touring at a time in my life where I dont get to ride as much and I ca have a new toy to play around with.

with a 3 year warranty too!
Ps, I go through this faze every Spring for the last couple years of thinking about a different bike but always stay with the RK. I am paralyzed by the thought of whatever I may buy will be disappointing compared to what I have and again, to be perfectly honest, I dont want to spend 23 to 25K on a new bike, just not worth it to me anymore.