No need for a strap, Bluetooth linked locks that are automated so when one opens the other does to. Or put the lock on the wall rather than on the door and have a mechanical device running up and through the roof to the other door, configured such that the two door locks are restricted similar to the automation.
This hotel was built over 100 years ago and was destroyed in a fire in the 1960s. The article isn't about how to actually solve the problem of locking shared bathroom doors... it's about sharing insights into how designers were better able to solve a problem by focusing on the objective rather than focusing on the implementation.
