Most relevant to Turkey is the fate of Syria's Kurdish enclaves. Somewhere between 10-20 percent of the Syrian population is Kurdish, creating a strong case for a greater Kurdish zone of control and eventual autonomy together with fraternal allies in Iraq, particularly given that the largest concentrations of Kurds in Syria live in the north along the Turkish border areas and stretching eastward towards Iraq.
What is more, Turkish, Syrian, and Iraqi Kurds (at least the ones that live in Iraq's northwest, across the borders with Turkey and Syria) are linguistically united. These Kurds speak the Kurmanchi variety of Kurdish, as opposed to Iranians and northeastern Iraqi Kurds. They speak the Sorani variety of Kurdish, which is more different from Kurmanchi than Portuguese is from Spanish.
Syria's Kurds would likely turn to Turkey for support. They would appreciate Ankara as a balancing force against Arab nationalism, a lesson they would fast learn from the Iraqi Kurds, who have made Turkey their protector against Baghdad since 2010.
This presents Turkey with a crucial choice. It has traditionally been hostile to an independent Kurdish state or entity anywhere in the region, lest its own Kurdish population make similar demands. But its calculus could be changed by the prospect of chronically unstable Sunni Arab neighbors, and the need to counter Iran's Shiite axis -- currently stretching from Baghdad to the Assad regime to Hizbullah in Lebanon. The Balkanization of Syria presents a once-in-a-century opportunity for Turkey.
There are more immediate reasons for Turkish support of an independent Kurdish entity in Syria. The shelling across the Turkish-Syrian border present an important case for why Turkey might be better served by buffer states such as Kurdistan, rather than the far-less defined geographic realities today.
Also, with Assad's authority collapsing most rapidly in northwestern Syria, he appears uninterested in preventing the usage of Syrian territory by the Kurdistan Workers Party (PKK) -- the militant group leading the fight for Kurdish independence in Turkey and perpetrators of numerous terrorist attacks there. Thus, Turkey ought to favor a new Aleppo-based government that seeks stability and order on its territory and that would act more responsibly, as Iraq's Kurdistan Regional Government (KRG) has, in reigning in PKK militias in northern Iraq. Indeed, Kurdish self-defense forces from Syria are now receiving training from Peshmerga forces in Iraqi Kurdistan.
Regardless of the Syrian Kurds' ability (or willingness) to reign in the PKK, Syria's main Kurdish political faction, the PK-affiliated Party for Democratic Unity (PYD), has learned from watching neighboring Iraq that Sunnis will likely unite against Kurdish self-governance. Thus, ironically, while the PKK would continue to fight Turkey, the group's Syrian franchise might decide to make friends with Ankara.