I really don’t see city kids applying in greater numbers (if you are talking NYC anyway), quite the opposite. Most NYC kids are not applying for academics, which are easy to find locally. They apply largely for sports or social life at boarding school, or possibly for family reasons. The first two are greatly diminished if almost non-existent this year. There are actually fair number of city boarding school kids that already came back home this year as they hated it, some possibly sent home for covid violations but others because they just hated it (and they are juniors who loved the school pre-covid). Several families from our old school that started applying put in on hold and are doing 9th grade in the city and then maybe applying for 10th if things are back to normal by then.
The PG thing is a different beast, there are so many kids that are trying to ‘reclass’ because they missed their seasons and are not able to get recruited and so want another shot at it. Boarding school is one of very few ways to buy yourself extra year of HS athletics so that definitely appeals, and I do know families that are serious considering both PG and repeating junior year.