"... politically it will be Chaosistan ..."

LR in Politico shares why even with an "arrangement" , we would be only buying time .... Here

"The [Elections Complaints Commission] ECC is withholding public announcement of Karzai’s vote tally which is below 50% ...  Most recognize a second round can be disastrous politically and logistically for all concerned and are looking for a solution, though in my view it is temporary. It basically kicks the Afghanistan political can down the road and really does not resolve the underlying tensions between Abdullah and Karzai supporters (Abdullah wants a parliamentary system of government, thus changing the constitution from a presidential to a parliamentary system). The tensions could erupt later in a much more disturbing fashion ...  

Abdullah wants a public announcement by the ECC that he forced a run-off and Karzai did not get above 50%. Then Abdullah will say, 'for the best interest of the country' he has decided to form a coalition government, this way he almost achieves a co-equal status with Karzai. 

Karzai wants no public announcement of the ECC results before the deal is finalized, if there is to be a deal. I think there will be some sort of a deal as Abdullah will use the opportunity to get his supporters in key places inside the system like pieces on a chessboard and await the next political power struggle which I suspect will be soon. 

The US is still pushing for a strong role for [former Finance Minister Ashraf] Ghani. In essence you could end up with three centers of power within the Afghan government. We may get away with it from a PR perspective for about six months. After that the dysfunctionalities will publicly reveal [themselves]. Ideally some would like karzai to run the political side, for Ghani and Abdullah to run the functional side of the government, but one cannot divorce the politics of a central government from the functions of the central government, especially in country as heterogeneous as Afghanistan and a country coming out of a brutal civil war; politically it will be Chaosistan."