Now that Apple announces that iPhone 7 and up will support full range of contactless smartcards from iOS 13 it will be possible to store your ssh keys on a yubikey or other contactless PIV card. I would really love to have support for this in Termius when iOS 13 comes this fall.

https://www.nfcworld.com/2019/06/10/362961/apple-to-let-iphone-owners-use-nfc-to-read-all-types-of-contactless-card-except-for-payments-cards/

Thanks!