The College of Clerks

Today's nomination of Judge Jackson makes me wonder if any future Justice will be selected without having previously clerked on the Supreme Court. Justice Sotomayor was the last Justice nominated without such a clerkship, though Justice Thomas and Justice Alito also did not clerk for a Justice. 

The Pope (at least in modern times) much come from the College of Cardinals. That may work well for the Church, but I'm not sure it's a great model for picking Justices.