A weird agreement would have to be found; the Syrian Kurds and the PKK can work together, the Syrian Kurds and Turkey would have to work together, but the PKK and Turkey just hate each other.
Quite unrealistic, the PYD is very close to the PKK and the PKK is numerically much more relevant. Additionally the military challenges posed by the YPG and even the IS are probably relatively controllable in comparison to internal unrest incited by the PKK or IS sympathizers.
During the last month Erdoğan has been quite successful in killing the peace process with PKK. If he starts implementing his idea with the buffer zone, he will create a second internal enemy (IS sympathizers). And internal strife has always been an optimal chance for coup attempts.
