When they have more passengers than they can seat with seat blocking in-place, they should treat it like a VDB situation and ask for volunteers to sit next to a stranger in exchange for a travel voucher. This keeps (hopefully) people who REALLY care about not sitting next to a stranger from having their worst fears realized at boarding and also allows gate agents the flexibility to fill-in blocked seats next to passengers that don't really care one way or another. Depending on the flight length, I'd gladly give up my 2-3 feet of separation from a stranger in exchange for a travel voucher.