Seeing a heroic Scholomance for example, would really bring some much needed nostalgia back to this game. I love what you guys have done as far as bringing back Deadmines and Shadowfang Keep, so some more of this would be greatly appreciated.
It would also be really good to see another 10 man raid put in, with an emphasis on the casual player. Kind of like how ZG was when it was first released. It was pug-able however it did take some wipes to learn the mechanics, and people did have to communicate in order to do so. I'd highly suggest keeping it away from the LFD and cross-server grouping as communication is very rarely to be found there. I mean, I'm in a 25m guild that's doing fairly well in the T11 content right now, but I still wouldn't mind seeing another 10-m raid introduced for something to do during off-time. Make it drop loot SLIGHTLY less valuable than comparative tier raiding, but still 359/epic quality. I think this would be a really great option, and a lot of people would enjoy it.
Hell, you could do this in the form of a heroic blackwing lair. It would suit the expansion well due to where we are story-line wise currently with cataclysm, with the whole twilight/black dragonflight madness going on. The only thing you'd really have to change would be the final boss. Obviously we couldn't fight Nefarian there as well as Blackwing Descent. Even though, if this were to ever be implemented, it would be content patches away and blackwing descent would most likely be an after-thought at that point.
I know, I know...wishful thinking, but you saw the amount of people who loved that nostalgia thread Bash created, with the patch notes from 1.10. All those same people would kill for something like this. Obviously NEW content would be better, as we haven't seen it before, but being able to keep creating new things, while giving the older players that touch of nostalgia, would be a win-win for everyone. You have the older players who fought there way through the old vanilla content, and would love the flashback to those days during vanilla, and then you'd have the newer players who never got to experience that content who've been wishing they did as they hear of it more and more from the old-schoolers.
I know plenty of people will disagree, and just want NEW content, but there will be more people who would love this. Just my humble opinion. Keep up the good work.