To do this now would plunge the Labour Party into turmoil when we need to be fighting a united front, it will cause widespread internal resentment, and if nothing else it is a desperate throw of the dice from the usual suspects, some of whom (and yes I am thinking of Geoff Hoon) are careerists who are disliked by a certain proportion of the Labour Party and are unpopular with the electorate.
The time to do this kind of navel gazing is after the election, the last realistic chance we have had prior to it was during the summer, when we had the expenses row. Not only that, it's hardly news that will plunge the Conservatives into disarray and despair.
I only hope MP's (no matter how desperate the situation and how frustrating the PM can be) will hang on. We need to win this election, because if we do not the Conservatives will further wreck the economy on a full Thatcherite drive (the usual economic policies that refuse to take into account stupidity and selfishness), deliberately change the Party expenses rules in a way that is aimed at destabilising the chances of Labour coming back, and cause no end of extra misery on the general public