I seriously doubt Miller can be trusted to write an iconic, all audiences version of the character which is what All Stars mission is supposed to be. Esepcially not when he' touting that it'll be part of his DKR universe. If this Batman is the psychopathic yutz from DKR and DK2 then I don't really have alot of hope for it.
Morrison and Miller clearly have very different agendas for their respective character. Morrison wants the Superman who had fantastic adventures where anything was possible and there was a sense of hope. Miller, on the other hand, has always written Batman as very dark and violent. I like both of those interpretations, as crazy as that sounds.
Miller is my second-favorite Batman writer, just below Denny O'Neil. I LOVED Y1 and DKR (but I greatly disliked DKSA). My only complaint with Miller's portrayal of Batman is that he makes him far too antagonistic towards Superman. The two should certainly argue over methods (sometimes even heatedly) but should always have a mutual respect and friendship with one another. Superman should admire the fact that Batman does all the things he does without any powers. Batman, on the other hand, should admire Superman for the hope he instills in people and for all the times he saved the planet.
That's just my opinion, though.