I think the biggest problem here is one not even mentioned: What happens when the information is wrong? Passengers swapping seats isn't all that uncommon -- I've done it many times to allow families to sit together -- but the computers aren't going to know that has happened.
On a recent flight I swapped seats with my girlfriend -- she wanted the window -- and the service director was clearly flummoxed by the fact that the man in front of her was "Elena" and the woman sitting next to me was "Colin". (I'm guessing that they've been told that they should never assume genders based on names, but she could clearly tell something was off.) In that particular case, the confusion was quickly remedied; but I can only imagine the embarrassment which would ensue if flight attendants start singing happy birthday to the wrong passenger.
We had a flight once where they had assigned my then six year old daughter to a seat on a separate row from the rest of us (me, wife and son) so naturally my wife took that seat and let me sit with the kids.
This was very confusing to the flight attendant. She was like "You need to sit in your seat!" to my wife and as we explained the error by the airline, she scolded us and said "but kids can't sit by themselves!" Uhm, no that's what we fixed... Rest of the flight she looked at us suspiciously as if we were up to something.
On a recent flight I swapped seats with my girlfriend -- she wanted the window -- and the service director was clearly flummoxed by the fact that the man in front of her was "Elena" and the woman sitting next to me was "Colin". (I'm guessing that they've been told that they should never assume genders based on names, but she could clearly tell something was off.) In that particular case, the confusion was quickly remedied; but I can only imagine the embarrassment which would ensue if flight attendants start singing happy birthday to the wrong passenger.