The advantage of storing time-based one time passwords (2fa TOTPs, the ones traditionally used in Google Authenticator) in 1Password is that it's convenient to let 1Password autofill the 2fa field.
However, some threat models arguably require users to physically separate their passwords from their second factor; in my case I've done this via a Yubikey.
Yubikeys store (up to 21 or something?) TOTP secrets. As is typical with smartcards, a computer can request that the key generate one token but cannot extract the secret (the one used to generate codes) from the key. Although there may be various attacks involving lying to the chip regarding the current time, using a Yubikey for generating TOTP codes is very convenient and arguably more secure assuming honest hosts.
If 1Password allowed users to autofill one-time passwords through a yubikey, they would be able to combine the convenience of 1Password autofill with the security benefit of using a physical, separate second factor device to authenticate.
I understand that this might be difficult to explain to users, however, so I understand if it is not implemented. It would be really nice to have, though
1Password Version: Not Provided
Extension Version: Not Provided
OS Version: Not Provided
Sync Type: Not Provided