The SD card while protected should allow copying of the book from card to reader but the point is the card is the delivery mechanism which is cheap and can be bought in bookshops, airports etc. The protection element is in the ability to read the book on another reader. That could be blocked while the book is 'tied' to a single reader. If one wants to share the book after having read it, unlock it from the reader and give the card to another person.

This doesn't stop online downloads of books too but it's the ability to buy books in the real shops rather than the online ones which would allow them to become mainstream. SD cards at very small sizes, enough to fit a single book would cost pennies to make in numbers.

As for the SD format, well if the reader has an SD slot then it's not going to be made redundent as long as readers exist to service to format.

Marky