Part of the problem is that “USB-C” is really just the connector, and there’s a whole raft of things you can do with it. For an iPad, I suspect a USB-A to USB-C cable will suffice. But if there were actual USB-C ports on planes, then people might conceivably expect to be able to charge their MacBook as well for example, or any of the other laptops with USB-C, which use USB-PD over USB-C to draw 45W or even 65W. Getting that to every seat is far less trivial then the usual 5W or 10W for mobile devices and tablets. There was an interesting Runway Girl article on that, which seems to be the go-to place for everything “Tech” on airplanes. There does not seem to be a real solution on that front yet, but ultimately I think we can expect the traditional power sockets disappear for USB-C - but that is a looong way off. We all know that airplane tech moves at a glacial pace (Empower or Composite Video anyone)?.

A bit like old 30-pin iPod connectors on a whole range of alarm clocks in “luxury” hotels, still all going strong!