A couple of thoughts…
Firstly, I genuinly believe that Johnson´s reasons are personal because he has a good relationship with Mili-E, and there have been no recent big revelations about changes to budget policy that could have worried him enough to resign.
Secondly fears of Balls-Miliband repeat of the Brown-Blair power struggle are groundless and unnecessary. There´s no secret agreement or deal, and having Cooper on the front bench is likely to make the pairing more stable.
Thirdly Miliband has shown brilliant and decisive leadership. Any surprise at his not offering chancellor to his brother is misplaced, David´s made it clear that he does not wish to be a member of the cabinet this term.
Fourthly I´m psyched for a Cooper-May standoff, I´m pretty sure Yvette is going to come victorious out of any tussle.