It's possible this may be on the roadmap for future development, and even possible thatThe feature isn't available for developers yet.
But something that came to me while I was updating one password today, and creating a new account, was that that Password suggestion button that a voiceover user hears above the keyboard, when it's selected and a login item doesn't exist for this site we are just told that one password couldn't find any logins.
To me, it would make more sense to not wasteTime or real estate by letting me know that it couldn't find any logins, and immediately prompt me to create a new password/username login combination for the site.
I didn't see a feature to add a new password usernameLoginItem from the screen as of yet, and hope to in the mirror future.
Note: i've disabled iCloud Keychane and am just using 1Password within password and accounts in settings.
1Password Version: 7.2 (70200002)"
Extension Version: Not Provided
OS Version: IOS 12 Beta 10
Sync Type: Not Provided