>you almost always are carrying your passport while flying.

What? Flying internationally is a rare event even for rich people (business travelers excepted). Most of us will do it a handful of times, or not at all. I'd estimate the vast majority of flights to be domestic. You just use the photo ID that's already in your wallet.

If you don't want to carry an additional object, just put it in Passbook on your phone using the airline's app.