All right I got to thinking about future patches and if Blizz goes according to inital plans (that can change), they intend for 3.1 Ulduar, 3.2 Surprise Instance, 3.3 Icecrown Citadel.      There is some fan speculation that they should throw another patch in there, 3.4 for Icecrown and have 3.3 as another surprise instance.    Well I'll get into more detail as I list things.    The point of this is for me to list down baddies and talk about them.

*** POSSIBLE SPOILERS ***

(so don't read this thread at all if you don't want those)

Yogg-Saron

3.1 - There are definitely signs that point to him being in Ulduar.   Corruption of key figures in Storm Peaks...   Sulphuric attackers (fire elementals likely so Old God controlled)...   Loken defeated in Halls of Lightning and stating a master...

3.2 - But he makes more sense if he were in Azjol'Nerub, down where Arthas and Anub'Arak faced off against a Forgotten One.   Where the cultists of the Old Kingdom are.   This is one of the speculations of the surprise instance.

Ulduar could merely have a lackie Yogg-Saron set up to run the place.   Ragnaros the Firelord!   Well, not really.  lol

Expansion - There's some talk where he could be set up as the next big expansion villian.   That either means we only poke his eye out and he comes back in a more full form, or don't face him at all.    But expansion villians need territory we can invade (and level in), like how Illidan was set up to be the inital villian cause he had Outland (yes finished off with Kil'jaeden), and Arthas with Northrend.     

I suppose he could be in the Emerald Dream, being close to Ysera he could be responsible for the Nightmare corruption.   It would be Azeroth but how it looked in it's original condition.   Though if we invade that and set up base camps and roads everywhere, dunno how that's gonna work.

Other thing I can think of is Maelstrom.  But it's probably a different Old God at work down there, doubt Yogg-Saron goes there.   Depending on source there's 3-5 Old Gods kicking around.   There's speculation there's one underneath Tirisfal (west part of it), and possibly one under Black Fathomdeep.

Deathwing

3.1 - This one would be out of left field but hear me out.   The attack of black dragons are pretty "sulphuric" themselves.   He was corrupted by the Old Gods, so could be working directly under Yogg-Saron now.   Then he'd be the corrupting force, either directly or via Yogg-Saron.

3.2 - But a lot of people are more inclined for Grim Batol as the instance with him experimenting with Twilight drakes.   Though I offer another location, Deathwing's Lair on Outland.   It'd have to be a new floating rock east of Hellfire, and gives us a reason to visit Outland again (like with KZ on Azeroth).

Expansion - Deathwing just doesn't seem to have a large domain we can invade.   Though they could always make one up by having him I dunno, conquer the South Seas or something.   Or expand upon his Outland base to be much larger than it probably is, like a 2nd half of Outland.    Or, being the Earth Warder he's supposed to be, can raise a new continent on his own, perhaps the chunk of Kalimdor he sunk into the ocean back when the Well of Eternity exploded.

Nozdormu

He's pretty much been heavily hinted at being the one behind the Infinite Dragonflight.   Back when he was created or something, the Titans did show him exactly when and how he'd die so he'd not get all abusive with his powers.   So his actions now could be interpreted as fighting that fate, ensuring that fate (saw he'd die by the hands of 10/25 would be heroes), or maybe just simple Old God corruption.

3.1 - Nothing really points at this.  Unless it's just a one boss encounter underneath Wyrmrest Temple or CoT.

3.2 - Probably CoT, or something in Crystalsong if he pops up.   I can only really see Wyrmrest as one boss encounters.

Expansion - Again this guy doesn't really have a large domain we can invade.   Though, an idea for this would be to make it entirely in Caverns of Time.    Either make it enitrely in the past, like seeing Azeroth before the Sundering.    Or have some weird amalgamation of zones in which each corresponds to a different time period.  The goal would be to fix all that to save the timeline.

Frost King Malakk

3.2 - Well only possibly this patch.  He'd be the leader of the frost trolls of Zul'drak.  Gundrak (deeper parts), is another speculated candidate for the surprise instance.  Not much more is really known about him beyond this.

Anyways, that's all for now, go go Lore Nerds!