Iran and Turkey support for Syria are the life line of the economic survival of the regime.
Let’s start by Iran. Iran may not see with a good eye the growing ‘moderate’ sunnni influence of Erdogan on Arabs. For them he may be trying to hikjack the ‘arab spring’ to make it a ‘sunni spring’.
He has already hijacked Gaza and Somalia by his very strong criticism at the UN.
Iran also is feeling insulted by the fact Turkey has accepted the NATO defense system on his territory.
I doubt very much they will dump Bashar Al Assad easily. Let us not forget that Hafez Al Assad was the sole Arab leader to support Iran during the 8 years murderous war against Saddam who, remember, was then supported by the whole of the western countries. Also Baath Syria has been a warrant of Hezbollah. Without its support Hezbollah would have lost the 2006 war.
It is also obvious from the western involvement in the opposition that any regime coming after the Assad’s will be pro-western, anti-Iran, which will mean a dangerous weakening of Hezbollah that could become a easy target to Israel seeking revenge.
These are very good reasons for Iran to keep supporting Syria even if they realize there has been excessive injustified deaths during the rebellion.
As for Sunni Arab leaders, I also think that most of them are having a growing resentment toward the Turks taking over the Arab causes as they were their: They all missed Erdogan’s speech in the UN where he talked about Arab issues: Gaza, Palestine, Somalia etc..
Therefore, if Turkey puts sanction on Syria, despite the animosity some Arab countries have against it, they may see it as another arrogant step from Erdogan. They will also see that he is aligning with the USA and Western power’s ‘desire to weaken Syria, while the Arab league and Arab countries have not called for sanctions.
In summary, I tend to believe that the moment Turkey will impose sanctions, some Arab countries and Iran will step in to help Syria, just to let Erdogan know that he should remain in his place and not interfere more than he is doing in Arab affairs.
I may be wrong, the psychology of many Arab leaders is often unpredictable and the geopolitics of the region increasingly complex.