Bill heard about Google Inbox and he usually tries to separate email into his categories. He wants to set an expiration date on unread email, so if he doesn't read it within a certain amount of time, it will disappear. Leo says that an expiration date would be interesting, but could also be complicated as some people would hate it. But he can set up his desktop client to delete email after a set amount of time.
Gmail does have automatic filtering and Inbox takes it to a new level. They bundle similar emails based on the user's activity. Users can also pin email so they can keep it. It's invite only right now, but Leo suggests going to google.com/inbox to request an invite.