Sure, the plan to pull out was based on an assumption about the election, but the US is bound by the Status of Forces Agreement [SOFA] to leave Iraq whether there is a government in place or not. So, even if this were not "perhaps the most defining promise he made when he ran for president," Obama really has little choice now that Iraq has its own political system.
While it is good to keep track of this as Iraq has fallen off of many radar screens, to set it up like Obama really faces a key decision here is a bit strange. Omission of the SOFA in the article is stranger still.
Further, there is very little discussion in the piece about how changing the deadline interacts with Iraqi domestic politics. One clear thing has been signaled of late--that the Iraqis still have their nationalism. They have begun making noises about too much Iranian influence and would be very, very turned off by a revision of the US decision to get small and then soon get out.
Is this the same kind of decision as the original war plan (cool declassified slides here)? No, I think not as it takes into account the realities of the SOFA, of Iraqi public opinion and politics, and of the limits of American power. That would would make it the anti-Bush/Rumsfeld/Franks kind of plan.