Well now that I know it won't be a European Airport (I confused it with the former secret project by FB) I think KSEA has very good chances, as Umberto said they might consider it anytime in future and the well known FPS "problem" wouldn't be as great as for other developers. Remember they also did CYVR which is in a similar ORBX powered region and that one works faboulus. However KSEA wasn't mentioned in the poll at all!!
The demand for KSEA is definitely there as you can see in various FS forums, so why not ;-) I would really appreciate KSEA (as well as KPDX) if it is an American airport!