The factions change their allied relationships; though we know the basic outlines. I do not see how you can implement any parliamentary ( other otherwise) type of government.
What does the Syrian army want? Will the Islamists accept less then an Islamic state? The jihadists-are they willing to lay down arms?
How about the regional powers - will they stop funding/sending fighters?
The best analogy I can come up with is a boiling cauldron of internecine hate and willingness to die for a 'cause'.
Any transitional gov't wouldn't have a chance, unless we got the regional players and the Russians to enforce a peaceful transition.
Just don't see it happening while everyone is trying to leverage their advantages; much less agree to cooperate