Even eeprom address space is not mapped in ram address space.
Plus, SD card is accessed through SPI.
Plus, how would you access all of an SD card space (e.g. 4GB) with the limited MCU addresses ?
I think you could, however, write a class with an operator[] that would take care of accessing the SD card somehow (perhaps reading and writing bytes in a big file). That would be quite close to what you want, I think.
I don't see /why/ you're trying to do this. IMHO too much abstraction is /bad/ in a resource constrained environment like an MCU.