Hi! Mr. Erik,
I am also not trying to pick a fight with you. Personally i respect you very much as I see you name regularly in this form and like your way of giving to the point and good answers.
Here my friend, what i was trying to say is that i think controlling EA pin to run code from internal and external memory is possible. just we have to be extra careful.
Also with care fully designed circuit and software there is no chance of "unexplained" failures, and if there is some "unexplained" failures its simply mean that it is uncomplete.