Those portals have something to do with the Green Dragonflight I'm fairly sure, seeing as how the ones in Feralas and the Hinterlands are both guarded by them.
The one in Stormwind I don't know of any plans for, but the one in Deadwind Pass is likely linked to Karazhan. Whether there are plans for an instance there or not is unknown, but for the lore fanatics out there it is the tower where Medivh lived. Given the lore surrounding the area, I'd be willing to bet it's an elaboration on the events surrounding the Dark Riders and the massacare of that fellow's family.
I've found
http://www.wowguru.com/previews to be quite enlightening on such matters.
EDIT: If you peruse the site carefully, you'll notice that it's possible there are events in that tower and in the necropolis over Stratholme related to the opening of the Dark Portal in the Blasted Lands and moving to the Outland (the remains of the planet where one of the earlier Warcraft games took place, as I recall). While it all seems like crackpot theories, he had information about Silithus up prior to 1.6, and now we hear that yes...Silithus will not only have a 40 man raid instance, but a 20 man as well. Between that and Blizzard's announcement of an expansion, well...I can't see it's without merit.
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You just keep on trying till you run out of cake"