I get the impression that this is more the next generation of Google Now than it is the next generation of Gmail. (Google Now is all about plucking out information from larger sources of data and bringing the most important stuff to the front as it's needed.)
I suppose I could see how this would be useful if you're using your smart watch or your phone and only want the most important facts, boiled down to their essence. (But then, doesn't Google Now already do that?)
Outside of that context, it doesn't seem like you'll ordinarily have both Inbox and Gmail open at the same time, because (as far as I can see) Inbox is just a way of better organizing and presenting the underlying data, whereas Gmail is more like the raw feed.
I suppose I could see how this would be useful if you're using your smart watch or your phone and only want the most important facts, boiled down to their essence. (But then, doesn't Google Now already do that?)
Outside of that context, it doesn't seem like you'll ordinarily have both Inbox and Gmail open at the same time, because (as far as I can see) Inbox is just a way of better organizing and presenting the underlying data, whereas Gmail is more like the raw feed.