The BBC would hate it. White upper middle class family, boarding school, ponies, hawks, hunting, people learning Latin and Greek, the landed-gentry Merricks, and not a single ethnic minority in a significant role, unless you count Miranda being Jewish.
It's impossible to think of anything less fashionable. And I fear that if you were to change all these details to be more "relevant to today's young people", the whole charm of the books would be lost.