Syria is geo-strategically, historically and politically the most central of Middle East countries, hence the over-riding importance of the conflict there. Yet any discussion of the regional implications of that conflict is necessarily highly speculative. Its points of departure are the instances of regional intervention and "overflow" from the situation already taking place. Turkey, with its open support for the armed Syrian opposition, is the leading candidate to establish "safe zones" or even "humanitarian corridors" that could conceivably lead to war. Ankara's growing rivalry with Iran is increasingly being acted out in Syria and is interacting with tensions between Sunni Muslims and Alawites/Shias not only in Syria, but in Lebanon and Iraq as well.
Saudi Arabia and Israel are also huge stakeholders in the outcome in Syria. They increasingly identify a defeat for the Assad regime as an historic setback for Iran's designs throughout the region, and therefore to their advantage. Israel could interact with the conflict in a number of significant ways, short of outright armed intervention.
These are all identifiable contingencies that the region and the West must somehow plan to engage. The unexpected and unpredictable are by their very nature even more dangerous. The Alawite/Baathist regime's inability to compromise over its hegemony virtually assures the failure of the ceasefire mediated by United Nations (UN) envoy Kofi Annan.