I think there are two different things to take from the OP:
1) a notification/reminder that the most prestigious US colleges are looking for such a "hook". T
2) a pointer to a recommendation for one particular course of action; in the case of the mother in the article, for keeping your child unswervingly to the path to excellence in just one unusual field, as their "hook".
(1) is surely useful if you didn't know this already, as if you don't know you don't have the option of reacting to it. (2) is more interesting. While I agree that perseverance is an important skill and would certainly encourage DS not to fritter all his time, the riding example seems to me to go too far. If a hobby seems like a good idea when your child is 10, and you make them stick to it to the exclusion of almost all else until they're 18, you risk never letting them meet the thing they'd otherwise have discovered at 12 that would have been their real passion. A certain amount of experimentation is surely necessary.
Even if things like Coursera don't catch on (if I had to guess, I'd guess that they will, but I don't know although I'm well placed to), education is increasingly international, and even increasingly carried out in English. I know (not least because someone pointed it out last time we had this conversation ;-) that for certain vocational courses like medicine and law it may be essential to attend university in the country where you want to work, but for most people it increasingly isn't.
This makes a difference: e.g. if you were priming your children to go to one of the most prestigious universities in the UK, you'd be telling them not to waste their time on anything not related to the subject they wanted to study, but instead to read around that in the greatest possible depth, do activities relating to it etc.
I think there will always be good courses at good universities for clever, well educated, hard working young people who have their own opinions and interests and the initiative to follow them, even if one has to be a bit canny about looking at more than the obvious options. I propose just to do my best to help DS become one of those desirable students, and we'll see what university options fit when the time comes.
