They Void Crystal from which the Ashbringer was forged, was brought over from Outland, I'm pretty sure. There's no history of Naaru's existing on Azeroth before the more recent Burning Crusade events.

That being said, I just simply think that it may have to do with the power of the people that reside there. When you force a lot of paladins and other powerful figures, that oppose the scourge into a small spot... you create "hope" and that may very well be enough to help ward off the Lich King and his minions.

I think the purpose of a lot of the reuse(especially for the Tempest Keep instance bosses) was to allow players to experience some of the encounters that they wouldn't have seen pre TBC.

I would expect to see some 5-man encounters in Wrath that are, in essence, scaled down TBC 25-man fights. Not only does that allow Blizzard to re-use content, it also lets people see some of the strategies required for the upper tier fights.

And it probably makes long-time raiders just want to kill the bastards more.

It is quite impressive how little they have used the Titan male (and female) model, I think. Its a very cool model. We saw Archadeus use it, the Uldaman Watcher use it, yet it was never used for any other boss or raid (correct me if I forgot one) in vanilla WoW or TBC. Maiden showed up for Kara and thats about it.

Gathering it was classed as a special reserved model that designers deliberately avoided using, given the special importance of the titans (even if it was going to be 2 expansions later and years after they created it for vanilla wow).

I personally found Sholazar very fun to quest in, even if it wasn't totally tied-in to the whole Northrend storyline (the Blues make no appearance and the Scourge are only in the extreme east), it had some fun light-hearted quests and the Oracles are fascinating (they remember the Titans, so to speak).

I expect a re-appearance of Deathwing this expansion. We have four Aspects whose locations are known/who are in game now:
Alexstraza (Wyrmrest)
Ysera (Emerald Dragonshrine [physically]/the Dream [spiritually])
Malygos (The Eye of Eternity)
Nozdormu (Somewhere in time, brief appearance at the Bronze shrine, probable leader of the Infinites)
Malygos' corruption doesn't sit well with me. Overuse of magic is what created the problems he supposedly trying to fix by overusing magic. I suspect that he's being manipulated by Deathwing, given that the Black Aspect has already been able to take from Malygos nearly his entire flight. It's also possible that the Old God under Azjol-Nerub is working its corruption. Katrana Prestor (i.e., Ony) is also missing from SW.

Ice Troll lore is interesting - particularly the Zandalari being totally apathetic about the fall of Zul'drak. I suspect a Gun'drak raid will give us some insight into the consequences of the Drakkari's actions.

To add a bit of specificity to the discussion on Father Inigo Montoy - he reappears as a Lich named Thel'zan the Duskbringer, in the Wintergarde Crypt just to the west of Naxxramas' new location. The quest is, I believe, Alliance only.

I'm beginning to wonder if the younger Hellscream might fall in the same way his father did. Saurfang certainly seems to suspect as much, as mentioned earlier in the thread, and corruption/moral ambiguity is a MAJOR theme in Wrath questing.

One thing that doesn't seem to have been discussed yet is Varessa Windrunner. Not only is she alive and present in Dalaran, she leads a staunchly anti-Horde faction there, effectively declaring war on Sylvanas.

The Vrykul's "curse" (i.e., humans) is an interesting bit. Why DID the Vrykul start mutating into humans, if not from the Titans? If the Titans didn't do it, who did? It's possible, I guess, that Ymiron is involved simply to manipulate himself into greater power.

Something I suspect we'll see as we progress into Icecrown is the corruption of major lore figures. The Wrath trailer, The Echo Of Ymiron ("this one isn't ready yet...they must grow more powerful") in HF, and the lich inside the Lifeblood Pillar in Sholazar ("Arthas once showed strength like this...perhaps his path is the one you will follow") suggest that Arthas' ultimate goal is not merely to defeat the heroes, but to turn and corrupt them much as he was. There are any number of excellent candidates for this, really any hero whose primary goal is vengenace.