Dunno about any of that ?
Ive been flyings the Airbus for 12 years only the Honeywell FMGS equipped version and its always had the EOSID feature .I think you are correct that it is a customer option ..
My understanding of the Secondary design was flexibility to construct alternative departure routings and runways before engine start and indeed I'm told that many colleagues in North America use precisely this function as they operate a lot from multi runway airfields .
Either way interesting stuff but I do remain surprised by the amount of people operating the aircraft equipped with this feature who have no idea what it is or its independence from whatever is in the Secondary .
Safe Flying to all .