A few months ago I flew across the pacific. I'd say half the passengers watched something on their own devices.

That ship, of fewer devices, has sailed.

This doesn’t make much sense. If there’s an explosive risk, then it’s going to be a huge risk over land as well, and it doesn’t make sense that they’d be increasingly putting outlets at every seat.

>If there’s an explosive risk, then it’s going to be a huge risk over land as well

However overland flights ( generally ) don't route up to 240 minutes flying time from the nearest diversion airfield.

Four hours is a long, long time with a cabin fire.

How does this fit with the trend of carriers adding WiFi?

The WiFi on planes is satellite and something like 256 Kbps with extreme latency. It works fine for light web browsing and email, but it's unusable for video streaming. Your options are to pre-load entertainment or watch what the plane has pre-loaded in the seat-back entertainment screens.

This is changing. Gogo has new technology that’s supposed to be up to 100 mb/s, though I’m sure real-world will be lower.