It does effectively. With Gmail at least, there's an option to register Chrome as the mailto handler. Anytime you click on a mailto link anywhere on your computer, it will open Chrome to the compose window in Gmail. And Gmail works offline, so it's not really any different from having a traditional email client built into your browser.

remember Opera and Seamonkey (and Lotus Notes) back when the all-in-one email/browser/cal/notes application concept was still kicking

> all-in-one email/browser/cal/notes application concept

You mean Emacs? All it needs is a good editor :)