Makes sense- always found it annoying when there was someone else you knew on a flight,but was seated elsewhere. As for it becomming a match making or social networking service, I could see there being something there. Although it begins a conversation on sterotyping people, because it would suggest people would rather sit with people of similar age-but in reality, some of the worst nightmare passangers to sit next too-have been my own age group.
At the end of the day, if its a service that can be offered-why not !!