You might look up Non-volatile SRAM as well. If I understood correctly, it's like RAM except when the device is turned off, it is on its own internal battery power which can last years so it has all the advantages of both RAM and EEPROM. (fast write, no number of writes limit, non-volatile)


link to Maxim's list

You could even OR the External Memory outputs with Program Memory outputs and write self-modifying code because MOVX and MOVC would operate on the same memory. (some consider this an advantage... ;)