I'd love to see Karazhan as a 5man. I wasn't there to do it when it was current content, but it's such a cool place.
Make Ulduar like 4 heroics. One for the siege, one for the Antechamber, one for the keepers, and one for yoggg, vezzax and Algalon.
Karazhan. Kind of.
The Karazhan Catacombs.
Beneath the Tower.
Raid: Ulduar and ICC Dungeon: ehm.. idk
Thank you Shyama <3Everything's amazing but nobody's happy
Raid : Ahn'Qiraj 40, since it fits with the actual lore and the old gods "rise".
Dungeon : Mmmm ... Zul'Farak.
zul'farak would be good.
I would have chosen Scholomance because it's always been my favorite dungeon, and then in MoP I got my wish and it's even better than before. Second would have been Scarlet Monestary, and I got a two-fer on that deal.
So if I had to choose another one it would have been Stratholme, which we got in Wrath.
Then it would have been Deadmines which we got in Cataclysm.
If I had to choose one for now though, it's probably Grim Batol. I hated how there was so much stuff underneath on the lower floors that you couldn't see or get to. I want to know what was down there!
Also it would be cool to finally figure out what's going on underneath Karazhan. Granted, I don't want the KZ raid touched at all, but I still am curious to find out what they're up to in the basement and why those poor folks were down there hanging upside down under the water and all that stuff.
Kara is my first any only choice for a rehashed raid. Only raid I liked enough to want to run again.
They could bring in a lot of cool fights and mechanics in the raid. They could get VERY creative!
to bad they fucked up infinite dragon flight so we have no real reason to COT a dungeon anymore
I would like a COT of Karazhan, keep the one we have, but do a COT version where the final boss is Medivh :P
AQ / KZ / TK (not too easy and only as raid, none of this ZG / ZA --> 5 man crap)
Blackwing Lair without a doubt.
I have fond memories of kara, but hope they never rehash it, leave it be. Although I love the haunted house theme, so would love something new along those lines, crypts maybe.
To just point out to a few people (jaylock in particular):
Nax 40man would never return nor its loot table. Blizzard admitted adding in Ashbringer (albiet corrupted and alluding to a way to cleanse it for a player) was a mistake.
As for people "deserving" loot and others who did not see Nax during vanilla etc not deserving loot. Frankly such a childish attitude to the game. How does someone having something effect you? I've done those places while they were current. Only a few bosses on nax downed before TBC hit and I came back and cleared that place during TBC with a few friends, had done BWL and MC zg/aq20 and had aq40 mostly on farm bar twins cthun etc.
As for LFR - its a great little tool, made for people who dont have time to raid in a guild setting to a fixed calendar and for people who may not be quite good enough to do normal mode raiding. It lumps those two player groups together and it works. I didn't think I would enjoy LFR but i've grown fond of it.
Onyxia as others pointed out was just put in for level 80 players as gift to celebrate wows anniversary. Nothing more. fighting her again in BWD was a story addition showing nefarions experiments.
I would really like Karazhan - in addition I would add crypts as a 5man dungeon and then have a portal/entrance to lower kara made as a new raid. Make some changes to normal kara to show the legions influence and then in lower kara you fight a shade of sargaras or something left behind by him.
Ahn'kahet The Old Kingdom expanded upon and made into a huge Ulduar style raid would be my first, second and third choice.
I hate Karazhan. I refuse to set foot into that dreaded place. The theme of that place is horrible.
ZA and ZG should be updated to 90, the unnerfed versions where one can't skip bosses.
And maybe Ulduar, as the first 14 boss dungeon for 5man.