And they still got Azjol Nerub out as a dungeon along with Ahn'kahet. So it wasn't entirely scrapped but rather used as dungeons.
Obviously Farahlon is irrelevant to the story when it never even happened. If Blizzard ever made Farahlon you bet yourself they'd make it relevant to the story. Heck, on the datamined maps there was iron horde structures on Farahlon. They obviously were working on Farahlon as They simply scrapped the sh** out of a lot of crap.
http://marlamin.com/minimaps/dreanorlocations.jpg
Blizzard f**ked up. There is no way around it really. This expansion has been 1 big miss.