to your point, not exactly a one-to-one, but several discount airlines (e.g., RyanAir, PLAY, Allegiant, Frontier, Spirit, Wizz, Flair, AirAsia) already require an app to check in for a flight, or pay a fee. No app (or the horrors, no mobile), it cannot be done on a regular computer, must go to a ticket counter and pay a fee.

This isn't a problem, these apps will probably run fine under emulators. It's only wildvine/play protect stuff that barfs.

They'll run fine until they don't, because they'll hook up to remote attestation "for sekhurity" like more important apps do. Not to mention, those apps' vendors don't particularly want you to run their apps in emulators either - there's no use case for this they consider not harmful to their business.

Maybe some, but certainly not all in the list. Neither Ryanair nor Wizzair need app, you can do everything in the browser.