Can you elaborate? How to use "QoS, metering and caps, etc." to enable people to pay for their usage?

You don't. Internet should be free. For an airport use-case, it should be covered from ticket prices.

That's not free, that's paying for it in a different way.

I do think the internet should be free, but how we sustain that is a pretty viable question. APs need to be installed, configured, and monitored. When spaces grow, APs usually need to be reconfigured or moved.

I know that airlines are fairly low margin businesses, based on what I've read from the recent bankruptcy stuff. I am curious about who owns airports and what their margins look like.