I agree for the most part. Surprisingly, even though you have that massive hole in the floor, the other areas appear to have more surface rust. But I wouldn't go by just appearance (we can agree the appearance is BAD). When I did my POR-15 work, everything looked like surface rust. The subframe itself was (IS) in great shape. But you know what happened to me. The mount/unibody closest to that big hole is definitely the worst. If any part broke off it would be that one first IMO.
POR-15 will definitely prevent most of those areas from getting worse. But the rust on the body of the car along the bottom edges of the doors/rocker panels, and that massive hole, would not make doing the POR-15 worth it if it were my car.
The thin metal plate around the mount on the left in the pic below is breaking as you can see. That'* part of the square plate holding that mount in. The mount that broke off for me had the same signs. But it'* hard to predict what will happen and when. Yours doesn't look THAT bad.