First igniting the Syrian civil was done by a coalition of US / EU/ Saudi / Turkey. People gotta realize US & Turkey was in this together in the beginning, only when shit hit the fan everyone started to pursue their own often conflicting interest. The only winners in this as of now are Russia, Iran and Israel. Turkey already lost big time, now what it's trying to do is cut its losses: stop the terrorist organization it has been fighting for the past 30 years to turn to founders of a neighbor state and get rid of 3.6 million refugees that it's unable to keep.
The idea in the beginning was to topple Assad rand his Shia minority ruling elite real quick and install a pro western (read anti-Iran, anti-Russian here) moderate conservative Sunni government as a part of the "greater middle east" project and "develop" spoils but it failed miserably. Erdogan & his sectarian, delusional foreign policy couldn't deliver anything to anyone, Obama refused to put boots on the ground and get in to another nation building adventure, Russia & Iran seen their opportunity & played their cards perfectly, US got pissed of and became allies with the only forces (YPG/SDF) that could deliver solid results(control areas where natural resources are). Now it's a bloody mess and there are no easy answers.
The thing is as capable and useful as they were against ISIS, asking Turkey to tolerate its 30 year old enemy PKK/YPG, an terrorist organisation to turn to border state is just crazy imho but shockingly that's what a lot of people in the state department & pentagon are saying. Ok I say good luck but I assure you that won't bring anyone any peace. %99 of 70 millon Turks, Nato's 2nd biggest army, Syria (Assad), Iraq and Iran won't stand for that but you wanna try go ahead.
My dream for the Kurdish question in Turkey would be PKK laying down arms and declaring the the days for politics through violence are over (ala FARC in Colombia or PLO in Palestine.) Violence and killing sadly only strengthen militarist, facists, racists and extremists on the both side and creates a self feeding loop of destruction.
For Syria everyone (including YPG) should be on the table, every group should lay down their arms, every player US / Russia / Turkey / Iran actually agree to stop the war of proxies but sadly no one (as can be seen int he example of old allies Turkey & US) really trusts each other and everyone is so eager to make the other pay no matter how short sighted that viewpoint might be.