U.S. potential engagement in Syria?

Watching GPS with Fareed Zakaria, on CNN, yesterday morning, I listened to two familiar guests to this program: Richard Haas and Anne-Marie Slaughter speak about the potential for U.S. engagement in Syria. Haas is President of the Council on Foreign Relations, a Washington think tank; Slaughter is a former director of policy in the State Department under Secretary of State, Hillary Clinton, now a professor of International Relations at Princeton. Both are responsible and not known for their radical approach to international relations.
And both are beginning to advocate for some kind of American intervention, beyond the under-the- table supply of arms to the rebels. They are talking specifically of a "no-fly" zone, with a rapidly narrowing window of opportunity, given the numbers of refugees fleeing Syria and the continual bombing of the "innocents" in that country by Assad.
We know more unambiguously from reports coming out of Vladivostock's APEC conference, that both Iran and Russia (as well as China) are unapologetically in Assad's camp, and there is increasing apprehension of the conflict as one that pits two camps against each other, not merely of two Islamic camps, Sunni and Shia, but also of two international camps, pitting the 'west' against the combined Russia-Chinese-Iranian axis (and likely the North Koreans for what that's worth).
What was a proxy war is likely to morph into a more substantive conflict, especially after the U.S. presidential election; there are just too many sparks flying not to ignite some kind of fire.
And the capacity of diplomatic maintenance of control, multilaterally, can and likely will last only so long, until the strong arms of more countries demand a place on the battlefield.