It is not impossible to desire that Bashar al-Assad should remain in power until ISIS is so drained by defeat in Iraq that the Syrian part can be vanquished by Sunni allies of the U.S. This is called a pipe dream. Last year, it had a little more reality, and even more the year before that. This is mentioned in the interest of understanding the trend.
Perhaps the strategists hope to deal with ISIS-in-Syria later. But the word “hope” should never be used in government except in the context of selection between alternative strategies. In this case, the strategy of training the “good” Syrian opposition has been more than overtaken by events. It has been run over by a truck. The loss of Palmyra describes a situation that could result in the partition of Syria between ISIS and Hezbollah.
With Iraq, useful adjustments to strategy are feasible, if victory, or achievement of strategic objectives, are replaced by the concept of contained chaos. In terms of any conventionally defined goal, the existing Syria strategy is completely unworkable. So tinkering will not work. There is a complex diplomatic problem to be solved. The Secretary of State who solves it will Vulcan mind-meld with the key players: el-Sisi of Egypt, Erdoğan of Turkey, Abdullah II of Jordan, Iran’s proxy–Hezbollah, and the U.S.
The above list includes people who might have done a bad thing or two to former presidents and journalists. It includes hostile entities, and unreasonable entities. In the context of established policies, these unfortunate facts cause any derived solution to be “unthinkable.” To whom it may concern: You’ll just have to deal with it.
No specifics can be offered, because the assembly of a pan-Arab army (with Turkish add-on) is a very human endeavor. For any other part of the world, my helpful suggestion would be lots of Havana cigars and Macallan Lalique 55 Year Old Single Malt.