@jon @Vivaldi
Somewhere in heard wise words: "do one thing and do it well"
So if Vivaldi is a browser, it shold be only a browser imho. No password manager no RSS feed, no mail, no calendar. Just don't. There are other tools for that.

What you are always welcome to do is to create an independent email app, RSS feed app, calendar, password manager... Whatever you like.. And if it integrates well with browser, awesome.
But we really need to be respect more this do one thing philosophy again