Ahn’Qiraj was a huge deal when it was introduced almost five years ago (January ’06). The build up requried players to collect a plethora of materials in the “War Effort” against the Silithids, before players were finally able to restore the Scepter (of the Shifting Sands) which could then open the gates to two raids, one 20-man (Ruins of Ahn’Qiraj) and one 40-man (Temple of Ahn’Qiraj). There was also an army of insects on the other side, but that didn’t last.
There were many things that made AQ’s injection into WoW unique, in good ways and bad. The bad, quite honestly, was just (at least) a guild that got the scepter and refused to open the gates on one of the servers (Eventide on Cenarius, I believe). Essentially, they held it hostage. I’m sure Blizzard learned from that. Fortunately, as I suggested, there were many good things involved in it that such a blemish is overshadowed -namely The War Effort.
In a rare moment, both Alliance and Horde players were working towards a common goal. They had to collect a tonne of materials before the gates could even be opened on the server (nevermind the previously mentioned Scepter quest chain). There was a relief effort NPC in every city and players had to keep turning in cloth and other items until the coffers were full. Let’s be honest, Horde and Alliance have some hardcore zealots who hate the other faction (despite the fact it’s simply a game), but the idea of working together to reach a common goal is exciting. It makes Azeroth the bigger picture for a change. Based on the design, it was also something everyone could be a part of. It didn’t matter if you were in a hardcore raiding guild, or even a guild at all. You could go out and do your part.
Of course, the actual gates opening was huge as well. Again, once your coffers were full and you had the scepter you’d ring the gong and the gates would open. Of course, the Silithids would be happy to attack anything and everything when that happened. But after all that was said and done and you went through the Ruins and then the Temple players got their first glimpse at something we’ve only encountered once since: an Old God. Even at level 80, you can wipe fighting him (though it’s usually because someone does something foolish). Still, 5 years later and we’ve encountered one other Old Gold, and that was in Ulduar. It makes these two bosses somewhat special that way.
So the question is, could such an event happen again? I think the answer is absolutely. Unfortunately, it won’t happen when it would make the most sense. If a Cataclysm struck Earth, humanity would spend most of the following years rebuilding and getting supplies where they are needed most -in theory (see Hurricane Katrina). As such, that could’ve been an opportunity in a few weeks. However, in terms of gameplay and business model, it won’t. Blizzard will want players checking out all the new stuff. Races, class combos, new content…all the goodies that they’ve been hyping for a year now. To roll new characters just to go and farm would be a waste (though half the gold guides online would tell you otherwise). But what about down the road?
I can’t honestly see Blizzard creating a section of Azeroth that requires unlocking again, least of all by player control. Having it on a timer would be interesting. Be it a tower, or something in a lake, or whatever option. It randomly appears and a few NPC’s (nay, Doomsayers!) elude to some knowledge of it. Then an honest invasion (per server) could occur and create a similar scenario to AQ. The after effects might involve some restocking (perhaps after someone like Sargeras showed up?…though, Deathwing’s already annihilated half the world) though.
The bottom line is having the Horde and Alliance set aside their differences on rare occasion is fresh and unique. I can’t see such a thing happening in Cataclysm because the two key elements being focused on are Deathwing, and the Factions renewed war with one another. But, the Horde and Alliance were also heavily at war five years ago.