The well-known PIC16C84 microcontroller was introduced in 1993 and included 1K of 14bit EEPROM code memory. I don't know how difficult it would be to include EEPROM in the FE310, but any 1993 patents have already expired, and even small EEPROM is very useful in many cases because it avoids the need for external memory. If Flash can't be included in an open design then EEPROM would be better than nothing.