It is "right quick", TMK, because it was taken away, then. KJV reading "is taken away from being a city" (not "about to be"), but your reasoning is still good as "about to be" means pretty quick, not 2500 years, later.
Isa 17:1 The burden of Damascus. Behold, Damascus IS TAKEN AWAY from being a city, and it shall be a ruinous heap.
"is taken away" - present not future.
soor שׂוּר סוּר
Jer 49:23 Concerning Damascus. Hamath is confounded, and Arpad: for they have heard evil tidings: they are fainthearted; there is sorrow on the sea; it cannot be quiet.
Jer 49:24 Damascus is waxed feeble, and turneth herself to flee, and fear hath seized on her: anguish and sorrows have taken her, as a woman in travail.
Jer 49:25 HOW IS THE CITY OF PRAISE NOT LEFT, THE CITY OF MY JOY! (NOT LEFT, gone, destroyed)
I don't believe Isaiah 17 figures into current events in Syria (or Isaiah 7-8 and Amos 1). We all know that Isaiah and Amos were contemporary prophets. Both Isaiah and Amos foretold that Syria and Israel would be destroyed and fall to the same opponent (Assyria). II Kings 16 reveals that the prophecies are clearly fulfilled. This is also confirmed by historical records.
"In 732 BC, the kingdom of Damascus lost its independence and existence, its holdings carved up into Assyrian provinces. Israel, on the other hand, was allowed to survive, albeit reduced to a fraction of its former size and cut off from the sea”
Source: http://oracc.museum.upenn.edu/saao/aebp/essentials/countries/israel/
A key point to the fulfillment of Isaiah 17 in Isaiah's time is the phrase "in that day" (17:4) Isaiah was saying that Damascus and Syria would fall in the same "day” that Israel would fall. The northern kingdom of Israel, fell in 722 B.C.
Revelation "watchers" today, say Turkey will invade Syria and destroy Damascus. Will Russia standby and watch? They are pretty annoyed regarding Turkey shooting down their bomber and this off the heels of losing their passenger plane coming back from Sharm el-Sheik. Many are saying Turkey is the modern day fulfillment of Magog from Ezekiel 38, but Magog is known by most Biblical scholars as Russia and Turkey is Togarmiah. So, I do not believe Turkey will be destroying Damascus.