Those rural routes should charge more for mailings to those routes if the sender wants to get it there. That would be my solution. It's not $0.81 or whatever for Pa Kettle out in Dogpatch, it's the full priority $7.85 (or whatever) and it goes out for delivery once a week. Medications and things can go FedEx like Medicare, or any one of a dozen other parcel carriers. Even my folks out in podunkia have internet services now.
There's also the problem of all those little offices. For example, in the area of PA I like to travel, there's an office in every little town - some of them no more than some dude's house where a room that's accessible from the road has a counter that's open from 9-12 every day and has some boxes in it. Consolidation is the key.