[Shank]

On iPhone, keys and transit cards that integrate with the system level Key and Express Transit systems work when out of battery as long as your phone isn’t intentionally shut down by you beforehand.

I’ve boarded trains and bought items in Japan with a “completely dead” iPhone using the power reserve feature where Express Transit cards remain available. It actually works really well, and means I don’t have much fear using my phone for those things in Japan.

Granted, ID cards aren’t like this, but there’s no reason why a system couldn’t be added for them.

[verticalscaler]

They have the same Suica type chips embedded in the Japanese iPhone models, big whoop. One can't help but eyeball a stupid and expensive phone and a hair thin flexible Suica card and shrug.

You could also cut that chip out and put it on a cute keychain. :)

[Shank]

Suica-support is not at all done via a special IC in Japanese iPhones. FeliCa is just a spec and JP model iPhone 7 added via a special IC, with iPhone 8 adding support globally.

Mobile Suica is far more useful than a physical Suica, with features like being able to review transactions on your phone, refill anywhere, add passes anywhere, and buy Suica green tickets, commuter passes, etc while not at a station terminal.

Good luck inserting your cute keychain into a machine for charging or performing basic Suica functions. You’re also completely locked out of commuter passes if you try that, because the machine needs to write that data physically on the card surface.