United Airlines starts serving passengers personalized ads on seatback screens

Well yes, that is what's next. Any terrible thing you would come up as parody, even the most deeply dystopian ideas are regularly proposed by MBAs to their bosses to tweak a bit more growth or profit. The only thing holding them back is not a consideration of good or bad, but whether they can get away with it. Sometimes that means they have think about customers, but for big entrenched, too-big-fail, not technically a monopoly but close enough they can act like one companies, its regulation. The airlines were deeply deregulated, and as we've seen with Boeing, even the safety side of aircraft regulatory power has been captured and and degraded.

They aren't allowed to charge for oxygen in an emergency. Not yet. But as soon as they can, in the name of free markets, you can be sure than some airline will make it an add-on.

Short of flying private, paying more doesn't insulate people from all the pain of commercial air travel but it sure insulates from a lot--but most people aren't able/willing to pay for it.