Has anyone gotten far enough to see any gargoyles, frostwyrms, or any demons, etc?

Pretty awesome. I've been inspired to bust out the old War3 level... a lot harder than I remember it being, my skills have unfortunately declined. Too much WoW and DotA .

The infinite dragonflight don't come into play with Thrall's escape until the very end. Most likely, it's the same here.

They influenced the course of the instance right from the beginning however, by capturing Taretha (who would have set up the distraction enabling Thrall to escape and so forth) which disrupted the timeline and required us to set things aright, we just didn't see that event played out to its conclusion until the end, where we rescue her.
On the other hand, the events described here sound basically identical to those in the WC3 campaign map, and nobody has mentioned a similar "oh no, [Insert Name Here]" is missing!" comment which would indicate something similar to Durnholde is going on here. The other CoT instances had members of the Bronze flight who would brief the players on what exactly the infinite flight is up to, is there no comprable NPC around the entrance to the Hyjal instance?

None that I saw, only remember that little blurb about how there's a disturbance in the timeline here and the Infinite Dragonflight is blocking the Bronze from the area (from the tour).

In the staging area for the raid, there's 2 NPCs, one vendors epic gem designs and has no dialogue, and the other is a giant tauren that sells consumables, also no notable dialogue (aside from humor).

So no, nothing really explains what we're supposed to be doing aside from participating in the defense of the World Tree until it is no longer Too Soon Executus.

It may just be as simple as the Infinite Dragonflight being a front for the Burning Legion. Possibility: Kil'jaeden is trying to change the outcome of the Battle of Mount Hyjal by interfering with the steps that led to the Legion's defeat. The dragons are just a front.

The only thing that doesn't fully jive is the infinite dragonflight wanting to kill Medivh in the Black Morass. There are a number of "goals" you can infer from this, but regardless of how you look at it that doesn't seem like a great plan for anyone aligned with the Legion.

Perhaps they want to stop the orcs from coming to Azeroth, thus preventing the orcs from defending at the Battle of Mount Hyjal? Sure, this would jive with the Legion's desires.

Or perhaps they want to kill Medivh to prevent his interference in the events of WC3 after being redeemed? Perhaps, but remember, Medivh is possessed by Sargeras at this point in time. The Legion would want nothing but to help him achieve his goals. If anything, they'd want to stop Khadgar & friends from "killing" the possessed Medivh in Karazhan. It seems that the Infinite Dragonflight has goals of their own, at least somewhat unique from the Legion.

Or perhaps they intentionally left out the "lore" NPCs for the PTR test.

I kind of have my doubts about the Infinite Dragonflight being Burning Legion pawns, even though it's a bit conspiracy-theoryish. The revelation that the Howling Shoals instance may be the fourth CoT instance at some point (suggested by assets in the 2.1 patch and a crashed boat in CoT blocking an instance area) points to the Infinite Dragonflight trying to meddle with events that don't have a direct impact on the Hyjal fight. If Arthas is foiled and never becomes the Lich King, how does the Burning Legion's attack on Hyjal see any benefit? On the flip side of the coin, even if Arthas is knocked off his block, why stop it other than for the sake of stopping it? The Lich King/Arthas isn't a major player in the current storyline and if Arthas never rises to power then Illidan never becomes a major player, but he doesn't start to have a major impact until after the Hyjal battle. At best it would be the Burning Legion preventing Arthas and Illidan from ever becoming powerful (with trickle-down effects of the Forsaken never coming to pass and the Scourge never getting loose from the Burning Legion), but that still doesn't stop their defeat at Hyjal which is the most critical turning point as far as the Burning Legion is concerned. Also what Grub said about Medivh being possessed by Sargeras at this point.

I would suggest that the Infinite Dragonflight are Old God pawns, since they are the ones that are most closely associated with the renegade black dragonflight and Deathwing, and any situation where their enemies never rise to power as Illidan and Arthas have is a better scenario for them to invade the world, even if it is in the grasp of the Burning Legion.

If Arthas were prevented from reaching Frostmourne, there is every possibility that the Scourge would just have eventually been defeated and the invasion of the Burning Legion never really begun.

Remember that it took Arthas to lead the Scourge to revive Kel'Thuzad at Silvermoon, contact Archimonde through the Blackrock's Demon Portal, and summon Archimonde at Dalaran. Ner'Zhul selected him for this purpose. The distinct possibility is that had he not been available or were otherwise held back, the Scourge would simply have been defeated on Azeroth.

So yeah, I don't think the Infinite Dragonflight is really a front for the Burning Legion in all of this if Howling Fjords is really the 4th CoT instance. Any interference from them at that location to disrupt the timeline would likely result in actually preventing the Legion from coming to Azeroth.

It does make some sense if they were agents of the Old Gods, because then they could prevent the natives from being as powerful as they were (by depriving them of one of their greatest leaders, Thrall), prevent orcs from bolstering the armies of Azeroth entirely (Black Morass), and prevent interference from the Legion in their own plans for Azeroth (potentially Howling Fjord).

Still no clue as to what they would want out of the battle at the World Tree.

Furthermore, this theory is bolstered by the fact that all of the twisted dragons have been results of interference from the Old Gods, from Neltharion/Deathwing to Eranikus and the Green Dragons at the Emerald Portals.

Do we get to recruit Furbolgs, jungle trolls and whatever other random crap you'd find hidden on that map? And its more likely that if the Undead never came then the main races would have never been forced to flee into Kalimdor to team up against the Burning Legion, thus the Legion's invasion would succeed and we'd all be demon chow.

I'd argue that Arthas reaching Frostmourne was far more critical in helping the Scourge break free from the Burning Legion. The end of the Undead campaign has some foreshadowing that the Lich King needed the Burning Legion to actually invade, and Arthas is the one that points Illidan to the Skull of Gul'dan, thus enabling him to slay Tichondrius and eventually. He's also a critical figure in the formation of the Forsaken. Additionally, Arthas never rising to power probably means the Blood Elves never join forces with Illidan (through Vashj) and then the Burning Legion.

You are there to test bugged content afaik.

If the undead never came wouldn't the human kingdoms just wipe out the legion invasion? Wasn't that kind of the point of the scourge, to turn all of Lordaeron into legion soldiers?

I'm not a big lore junky... yet.

It seems like the Infinite Dragonflight wants to stop Thrall from doing... something. They wanted first to stop his escape from Durnholde, and subsequently stop the orcs from getting into the world entirely. And at Mount Hyjal? What if their goal is once again to see Thrall dead? We don't know yet. Its entirely possible that in the future Thrall is the one to finally thwart their dastardly plans. If Howling Fjords is the fourth CoT... Well, I'm pretty sure Thrall wasn't there. :\ Has Thrall ever faced Arthas? I don't think he ever has.

The real question is: what invasion?

Without Arthas leading the Scourge Ner'Zhul created to actually fetch Medivh's spellbook and defeat the mages of Dalaran, there would have been no invasion. The agents of the Legion already present (Tichondrius, mostly) would not have amounted to much had the Scourge not been entirely successful.

With the recent lore found regarding Deathwing, it wouldn't surprise me if he was behind the infinite dragonflight.

I'm also inclined to believe that the infinite dragonflight are there to make sure Archimonde succeeds in his goals, not to kill him. It would be pretty silly to do that because then the Night Elves would retain their immortality, the Horde would still move on to become what it is today, and the Alliance would also stay intact. On the other hand, if the infinite dragonflight lends Archimonde a hand, and he succeeds, the world comes crashing down.

That isn't what I meant. In the initial stages of the invasion, the Scourge were controlled by the Burning Legion. I don't believe Arthas is critical in the least to opening the portal for Archimonde, the work of resurrecting Kel'Thuzad would have been accomplished by a Dreadlord eventually (delaying the invasion of Kalimdor may have allowed enough time for the defenders to defeat Archimonde in a different fashion, but I really don't see how). The defeat of Archimonde at the world tree was the impetus for allowing the Lich King to break free of their control and become an independent player. Without Arthas and Kel'thzad facilitating certain things along the way it may not have played out in that fashion, and the Scourge would have simply rolled over the defenders on Kalimdor and Ner'zhul would still be a Burning Legion pawn.

I was under the belief that Ner'Zhul and the Scourge were there to simply pave the way for the Legion and then they come in and mopped up, in much the same way they planned to use Gul'dan and the Orcs. There doesn't seem to be much stopping them invading at any time they wanted.

It does smell of Deathwing due to the the fact that his other daughter mentions "Master's work continues" in a screenshot and they are using Nether drakes and dragons to some end. But what would Deathwing gain from destroying the world? Even if the new dragonflight is his creation.

Destroying the world has been Deathwing's M.O. for a good long time now. He's so insane he doesn't even care anymore.

The Legion wants to destroy the world, but Deathwing wants to control it. He wants everybody to bow down to him (which was why he created the Demon Soul in the first place). How assisting the Legion to defeat the lesser races helps to that end is anybody's guess. Maybe he thinks it'll be easier to defeat the Legion when they're weakened from fighting.

The balance is so bad it's actually possible to completly destroy the enemy bases, breaking the script pretty badly. Sitting there for half an hour doing nothing then watching a cinematic where they go "oh noes, our base is gone, kill the tree!" is stupidly funny.