I'm too controlling over my inbox for this I think, it scares me to think about an algo deciding what I should focus on.
I tend to go full circle when I think of an app like this and go beyond Email, to think about "What should I be focused on today" which is much deeper, then I think about Getting Things Done by David Allen, and next think you know I don't install the app as I think i want the control?
Maybe I'm wrong though and an algo would be better