I noticed something odd about the Tyranny of Dragon write-up on the WOTC D&D page.
http://dnd.wizards.com/dungeons-and-dragons/story
I think it's a little odd that the third paragraph notes that the dragons are looting, enough to throw the region into chaos.
This seems strange as it's written about like this is a goal of its own.
The looting isn't a side-effect of conquest or of the search for the dragon masks (as you'd expect).
Notice it's set off "Meanwhile...." so it's not part of what the cult is doing. Is this information just given to tell us what the evil dragons are doing and that this is different from what the cult has going on?
It just seems strange to me to have a set up that is: stop the return of Tiamat, stop the conquest of the area by the Cult and evil dragons.
And then, dragons are looting!
Kinda weird way of presenting that information.
I can, to myself, make some sense of it...it's dragons collecting stuff to glorify Tiamat and to, perhaps, search for those mentioned Dragon Masks or totems or whatever.
I'm curious what they were trying to say here.
Anyone else notice the weird wording?
I'm not seeing the strangeness. The dragons are looting in order to amass a suitable hoard for Tiamat.
I guess it was just me then.
I was thinking that completing the ritual to return Tiamat and conquering the area would take primacy over looting. The way the blurb is written it sounds like looting is the main thing the evil dragons are doing.
I was just expecting the looting to be more opportunistic and incidental.....and not a focus.
When you put it that way, it does sound strange. Of course, that's not the impression I got from reading it. 
I'm sure we'll see the dragons doing more for the cause than looting. It would be a pretty poorly written adventure, otherwise. I think it would be an excellent way to first encounter a dragon, though. You aren't powerful enough, at low-levels, yo be seeking the troublesome beasts on their turf; but you might be in town when one drops out of the sky with pillage and plunder in mind. That could be a cool scene, and one I wouldn't be surprised to see kicking off the adventure.
I just misread or more accureatly misunderstood the text. My mental hiccup I guess...
I think you are on to something with your encounter idea of a dragon swooping down "commando raid" style. I can totally see that being in the module.