I have a very hard time seeing Blizzard giving the Alliance Gilneas again simply because of the area it borders.
I don't think there's a problem with it. If anything it gives the Alliance a faster way to get to the minigame in Hillsbrad as well.
Would you just fill it up like Bilgewater Harbor with a series of nameless people with the odd familiar name thrown in?
Depends on how nameless they would be exactly. For instance I don't consider a character like, say, Tobias Mistmantle to be nameless. Nor do I consider other important characters that played a very integral part in defending Gilneas during the Worgen incursion and then later the Forsaken invasion to be nameless either. Much like how the goblins got to meet up with all their old companions that helped them through Kezan to Lost Isle and now you meet them in Orgrimmar and Azshara, by comparison the Worgen only meet a fraction of that many characters and I feel that's wasteful because they had so much... well, character to them.
Reintegrate the former NPC population of humans from The Howling Oak? Would the Oak just be left empty?
In my mindset, the Howling Oak strikes me as a temporary refugee district. In all honesty this has been said before, but the Howling Oak is simply unrepresentative of the identity of the Gilneans and if anything I still have that feeling that it's just a placeholder area until something better comes along for the Worgen. If it does become empty then I think that's fine, but I wouldn't mind that it still housed certain feral worgen that still needed to go through with the ritual in case they never could in Gilneas.
What about the Stormwind dwelling Gilneans like Celestine?
Celestine is too busy in Hyjal.
Include Worgen and human in happy cohabitation?
Sure, why not.
Would consideration of other formats work... like Making it a daily hub for both factions? A new Wintergrasp/Tol Barad?
I don't know about both factions, perhaps I would be okay with it if the Alliance had a sizeable portion of Gilneas whereas the Horde were more situated in the outskirts planning assaults. As for the Wintergrasp/Tol Barad idea, I am completely unsupportive of anything of the sort simply because both Wintergrasp and Tol Barad have been known to fail by design concept.
When I say too much potential, I mean for example: Gilneas is restored to the humans and they are giddy to retake power in the region. However, when Greymane returns he sees Crowley sitting in his chair, as he's led the the people in Genn's absence and ran the area's defense. Memories of a not-so-long-ago rebellion kick in at the thought of Crowley having had such authority. Gilneas enters a state of political turmoil shortly after the people return. Royalists, rebels and ferals cannot be expected to get along for long even in the face of adversity. Interesting for story, but what would they do in-game? Make everyone happy or show tension. If they do one thing, they might anger part of the player base who want political intrigue/scandal and if they do the other, they make a similar problem but for other reasons.
This is indeed and interesting thought and I commend you for bringing this up. I personally feel that some tension would moreso arise from priorities in what the Alliance needs, I would like to personally see Genn opt to gain Gilneas back and wager that it would be a brilliant move to do so. Some disagreements could be made as the Alliance is pressured in many different strategic points, which would fire Genn up to support it even stronger. Between Darius and Genn, they have mended their broken bridges so I don't see too much conflict arising from them which I think I'm pretty fine with because these have to work together. If it's portrayed as anything like it was in the Gilneas starting area though, I would like that too.
What stops the Battle for Gilneas 2.0 from being identical to the first one aside from the lack of Liam?
Well surely there's lots of different ideas that we could culminate for this. Perhaps the Gilneans have more than just guns, steel, claws, and teeth to fight back against the Forsaken? Perhaps they found a much more rallying leader to help them against Sylvanas and her ilk? Perhaps... quite frankly, they're simply fed up with losing the kingdom they once loved and now are fighting back much harder with increased strength and furor. Who really knows... I personally think something different could be made.
Do the Alliance get an epic quest chain that leads to resealing the Greymane Wall?
I would hope so.
What would the Horde get in return?
I believe they would also get an epic quest chain in helping the Goblins gain Kezan back. Why do I think Kezan isn't completely lost? Well I think Thrall would have say in its restoration given that the Goblins saved him from capture and I'm sure the jolly green guy wouldn't have a problem in repaying them by restoring their home.
You must also remember that while Goblins have lost a lot, it hasn't harmed their identity quite nearly as badly as the Worgen. They still have a massive presence and a very vibrant questing experience due to many zones having Goblin settlements that they can easily identify with given Kezan's close relations with other cartels.
Genn only returned to the Alliance because Gilneas was lost and has always been more isolationist. Has he changed in his elder years?
He very much has, if you've read Wolfheart he and Varian are pretty much broski's now and Genn has learned much from his past mistakes after the death of his son. He is pretty much a humbled man whom I believe will stick around with the Alliance given that they've helped him even when they've seen the worst of him.
And why would Gallywix even WANT to go back considering Azshara was always his dream to rule?
For this I am unsure, as I believe that Gallywix is not in a very good position of power given his traitorous ways and being at the mercy of the Goblin players. Perhaps if Thrall or even Garrosh wills it, he will listen and also wish for Kezan to return.
TL;DR: Who would cross the Bridge to Gilneas must answer me these questions three, ere the other side he see.
Questions answered, hope I remained nicely consistent and well thought out for you good chum.