Patch 2.1.0. That's a LONG time ago... :D
Recycling content is nothing new in Azeoth. Whether it be mobs, abilities, or entire instances (ZG/ZA anybody?) nothing is beyond the realms of re-invention for the sake of lore progression and 'new' content. This time around, however, Blizzard appear to have subtly changed the ground rules.
The data files for 5.1 are showing scenario information for, of all places, the Black Temple.
Outland never really sat well with me initially, until I fully understood the lore significance of the planet destroyed by the Burning Legion and subsequently ruled by the Night Elf who began his life on Azeroth. I will never forget the feeling of genuine amazement I felt when I made my way to Shattrath for the first time and discovered the extent of Illidan's reach. However, for many of those who have joined the game since TBC, this mystical place is just somewhere you visit to get from 60 to 70. It is extremely gratifying therefore to see Blizzard not only revisiting the expansion, but re-writing the lore back onto itself.
I am aware that spoilers for exactly what goes on are already freely available, and I'm going to do my best to avoid them until time: needless to say I can speculate on what might be sending us there, and that Garrosh may have more than a little to do with our motivations. The video above shows the significance of the Temple to the Orcs: I wonder if the leader of the Horde is making deals he will regret later... but I'm more concerned with the significance of revisiting the Instance itself. The Black Temple holds a special place in many a Classic Raider's heart, for the fiendish nature of the encounters and the (frankly beautiful) armour and weaponry that the instance would yield. Part of me is hoping that we'll not simply get updated ilevel Blues as rewards, but perhaps the chance for replica gear from this place that won't cost 10k and require Black Market AH access to obtain.
Then there is the question of where we could end up next: I cannot believe that this will be a one-off incident. With a wealth of potential content ripe for recycling, will we find ourselves dropped into Karazhan again soon? How about a Ragefire Chasm scenario to uncover the truth below Orgrimmar? The deal with Pandaria has been brilliantly to combine questing inside available instance locations: introduce you to the Temple of the Jade Serpent before the location changes under Sha control and you need five friends to deal with the consequences. Does this mean we may yet have quest content for L90's in Outland and Northrend? I am genuinely excited by the possibilities these potential changes are presenting, where the only restricting factor will be the existing storyline. If we can keep this all within the auspices of existing lore then anything is possible...
Don't forget, we don't as yet have a Caverns of Time-linked instance location... :D