I'll use an example to explain my suggestion:
Ghost Browser has a concept of "By Project" and "colored tabs per Session".
So you can login in more than 1 Facebook account, or Gmail, etc, only opening new tabs sessions.

Firefox was it as experimental, called Containers. And there's a plugin for Chrome called SessionBox, but this kind of tool works better if it's a native tool and not a plugin.

I think it's so useful for people who manage marketing account for multiple clients, technicians, and for who has needs to have more than one active login in one website or social media.

I think it should be a great implementation in Opera and a step forward comparing with the other browsers!