“If you were designing an aircraft would you wire mission critical networks to a box in the passenger seat?”
Well, one thing to consider is: how many commercial aircraft were designed before there were computerized in-flight entertainment systems? They’ve added those systems and other computerized systems over the years, as patchwork upgrades I bet. So, if you are adding to an existing design, you might be tempted to “piggyback” on some existing components instead of keeping everything separate. Cut down on the costs and difficulty of the modifications.
It sure is worth considering!
My understanding is that all entertainment systems are air-gapped from control systems, meaning that there is no physical connection between them. They only share power (if that). If you hack into the entertainment system it gives you no access to the control system.
http://www.cbc.ca/news/technology/hacking-into-a-plane-s-controls-no-easy-feat-1.3042166
Just for fun, here is a video of retrofitting a commercial jet with Wi-Fi.
https://www.youtube.com/watch?v=OsuvlmDWYuA