Library 4.0 is when libraries don't truck in books anymore, as we know books now. Library 4.0 is the library after the widespread integration of smart objects and the "Internet of Things". Post semantic web. When atoms start schlepping usable bits.
Library 5.0 is a nonsensical term at present. So you can talk about previous library 'versions' up to 4.0 rationally, but beyond that we start to slip into the ontological bleed of the techno-social singularity.
Back to work.