In the speech, Miliband speaks approvingly of open primaries. So, why not use an open primary for the post-election leadership contest? It would be a way of saying that post-defeat, Labour would look out not in. It would also guarantee that the contest attracts national attention, something that is often not the case with opposition leadership elections—remember just how little coverage the Tory contest in 2005 got. The electorate would feel engaged with the question of what kind of party Labour should be. Finally, it would ensure that Labour picked a candidate with national not sectional appeal.
I suspect that Miliband is not confident enough in his own relationship with the Labour party to suggest such a move. If he did, it might well be seen as a sinister Blairite plot to reduce the influence of the party still further. But a candidate with better Labour credentials than Miliband, would be well placed to make this call.