Assuming that this one pre-condition has not changed, i.e., Paki army and US interests coincide in having the paki army's nukes aimed at India, then the IS is an interesting new variable.But It occurs to me that the Paki army's survival plan ensures keeping nukes aimed at India alone and reassuring the US of this fact. The US would be quite happy and grateful for that
The paki army can either try and coopt the IS by unofficially allowing them control of NWFP in exchange for oil or some such barter, and this will allow a nice new tumor to grow in pakistan's along with all the old ones.
Or the paki army can try and resist the IS and kill all those entities that are switching over from pro-paki-army terrorist groups to the IS -- this seems harder as the ones switching sides are at the footsoldier/cannon fodder level.
But all this maybe irrelevant if the IS mofos do not really want to (or care to) expand out of the middle east into Pakistan at this time -- this is very likely given how little the Arab islamists care for the low-grade paki islamists. This increases the possibility of some them outsourcing IS propaganda and recruitment in Pakistan to some paki group, and the best entity of that job is the paki army, who are experienced in running a criminal mafia with a religious front for many decades now.