Now war has openly broken out between the Free Syrian Army and the jihadist nutters such as the al Nura front.
So it is Assad Vs FSA Vs Islamic Nutters. A 3 way fight.
This means that the civil war has started before the revolution has been won!
The nutters are trying to create an extreme sharia theocracy (which Israel does not want as a neighbour!). The FSA want a pluralistic democracy (supposedly). Assad wants a brutal family dictatorship.
This makes intervention by USA, EU, Turkey and Israel vastly more likely.
Firstly because they don't want the nutters (or Assad) to win.
Secondly because they can now support the FSA with minimal danger of leakage to the nutters.
The biggest initial effort will be to diplomatically isolate the nutters. This means politely asking Saudi, Qatar etc to stop sending them weapons. The CIA will also be working on the ground to ahieve the same purpose.
Next the FSA will get lots of nice shiny Gucci kit.
Next the USA will follow their normal MO and throw drones at the problem. A few drones based in Akrotiri, Turkey and Jordan would very quickly make a huge difference. Obviously the integrated air defence system will have to be degraded so some SEAD would also be necessary.
A no fly zone is possible but would be very expensive and problematic to maintain.
Israel has already intervened more than widely publicised. Mainly to neutralise Assad's Gucci kit. The new situation makes them more likely to ramp up such activity.