Restricting the cruise level to FL250 or below considerably reduces the passenger oxygen requirements but obviously has significant fuel penalties.
Obviously freighter aircraft are only used in extenuating circumstances for passenger flights and the seating shown appears pretty comfortable compared to previous emergency flights.
In 1974 a Qantas B747 carried 674 pax and 23 crew out of Darwin following a devastating hurricane and in 1991 an EL AL B747 freighter carried 1086 Ethiopian Jews to Israel.