But how many public data breaches has SIA had?
If I was going to implement facial analytics using the IFE I'd definitely do it during meal service. RFID or wifi on the trolley to be able to correlate it's position. Take a photo snapshot once every 30/60s and then run through it later to see how people react to getting or not getting what they wanted. Bonus points: track the crew at the same time and make the happiness quotient part of their KPIs. and then maybe ask their union if they are cool? Cool.
No point doing it during movies unless you want people to be able to skip to the good bits, like one of YouTube's competitors!