Don't think they can. Keychain is supposed to be a secure storage solution, so I can't imagine they want users to be able to view that data, and it would be hard to manage it without knowing what it was.
That said, I found a post from last year saying that they would like to phase key-chain persistence out at some point, but it was fairly free of actual commitments.
> Keychain is supposed to be a secure storage solution, so I can't imagine they want users to be able to view that data
This seems at odds with the fact that macOS comes with a built-in app called "Keychain Access" that allows you to view the contents of the keychain (including iCloud keychain).
You can set some expiration linked back to the app that created that pair and when that app goes away that invalidates that pair, or have app related containers inside the Keychain that also get removed with the app. It is an implementation detail.
That said, I found a post from last year saying that they would like to phase key-chain persistence out at some point, but it was fairly free of actual commitments.