Will this ever be possible?
Right now you need to know the website first.
I'm not sure what you mean. Do you want to open 1password, then select a site and have it open and autofill in Safari?
Indeed, Safari doesn't allow extensions to open websites, and even if you open a website from 1Password or another app there is simply no mechanism available to invoke filling at that time. As far as "Will it ever be possible" though? Only Apple may know. It's not something 3rd party developers have any insight into or control over.