You've have an interesting idea, but it's not very practical. But don't worry, infirm and old people, as well as passengers traveling with young children are not seated in exit rows. If they are, it's my understanding that FA's are required to have them moved to a non-exit row seat.

In an emergency, if time permits, I'm told that FA's will move deadheading or non-reving crewmembers and other trained emergency workers such as police, firefighters, etc. into emergency row seats.