If KSA hasn't deployed their troops, what makes u think Pakistan will employ theirs? Your army being Sunnis will never support Assad and Hezbollah in flushing out isis
Saudi Arabia is a whole other story. They have an incompetent military; my brother served there as an advisor and apart of the Pakistani contingent and would tell me about them - they also have their hands tied in Yemen where they have been humiliated by Houthi insurgents. The Pakistan Army on the other hand is experinced, battle hardened, well equipped and know how to deal with Daesh-like militant groups.
Turkey is a Sunni country yet they have deployed their military in both Syria and Iraq against Daesh.
Pakistan has recently been getting closer to Russia while China and Iran who support Assad's regime have close relations with Pakistan. The objective will not be to support Assad or Rebels; it will be to combat mainly ISIS - we need to cut the root before the tree grows further.
Also, our army is not "Sunni". Once you join the Army, you are indoctrinated to cut all ethnic,tribal or sectarian links. Nonetheless; 'Shias' make up a very large portion of the Pakistan military.
Pakistani intelligence has already apprehended or killed a bunch of Daesh commanders in Afghanistan and along the border. The Ameer Khorasan (leader of Daesh operations in Iran, Afghanistan, Pakistan and India) has also been killed. Most of these Daesh are coming from Afghanistan; so Pakistan is increasing speed on the construction of the Durand border wall.
(This was from 2015)