Poor old Jeremy. He always looks a bit befuddled by what's going on. Either that, or he's the Millwall of party leaders.
Re-importing Miliband D would scare the shit out of the Tories but (a) he seems happy where he is (b) he's probably named in the Chilcot report (c) he is a firm Remainer but might not want to take the risk of standing on that platform (though could probably win it, after another couple of months of pain, if he did a deal with the SNP and LiBDems). Oh, and (d) Labour are such a shower of talentless bastards right now that he wouldn't be able to put a front bench together.