Looking at contemporary invasion map I can only think that this invasion plan could not be replicated today.
The invasion of Lebanon by forces in Palestine, today's Israel, look remarkably similar to the 1980s Israeli invasion and occupation of southern Lebanon. This could only end in out right war between Hezbollah and Iran against Israel across the globe. Note how the British base in Haifa was the targets of raids. Today that city would be pounded by Hezbollah missiles.
Any invasion from Jordan would go through Dara and not the Druze territory of al Suawida. The Druze lands have been largely untouched by the war due to their hilly terrain and Druze neutrality. Dara meanwhile is a major node on the road between the border and Damascus. A large battle is currently on-going between rebel and regime forces there. Any southern campaign would have to confront the Syrian Arab Army in Dara before moving north.
Neither Baghdad-administered Iraq nor the Kurdistan Regional Government would allow a major anti-Assad operation from their borders. The KRG wants to promote a Kurdish agenda while the Arab regime and Arab opposition destroy each other and Baghdad is openly pro-Assad.
Turkey was neutral in World War II so there were no forces invading Syria from it. Now, however, any anti-Assad invasion would need to help rebels in the north, especially with the major city of Aleppo.