Syria is likely to be one of the four nations making up the future Sunni Confederacy which is the main player of the Third Signpost. But for Turkey to ally with Syria, Assad has to go. This is because Sunni Turkey would ally with a Sunni Syria, but not with the current Shia regime at the helm in Syria.
In addition to various factors working against Assad, such as ISIS, Obama arming Syrian rebels, and Turkey figuring out how to remove Assad as well, another problem has been reported recently: Assad is running out of soldiers. According to this article Assad’s army has fallen from 315,000 in March 2011 when the civil war started, to 150,000 now. At that rate of decline (on average 3,600 soldiers lost per month), Assad will have no soldiers remaining by about the summer of 2018.
Of course losses like these are never linear, but these numbers over that time span points to a basic problem in mathematics which points to Assad being done very soon. The manpower pool available from conscription is shrinking and there have been many casualties as this Reuters article reports.