“Why didn't they just ride the eagles all the way to Mount Doom and toss the ring in the volcano?”
Nearly every Lord of the Rings fan has asked that at some point, and there are a number of theories addressing it, ranging from “That's stupid” to “That was actually Gandalf's plan all along.” The real reason, of course, is that it made for better drama for the Fellowship to have to walk all the way across Middle-earth instead (though I'm sure Peter Jackson could have found a way to stretch an eight-hour flight into 12 hours of film).
I had similar thoughts during the Zhaitan storyline. Here's the Pact with megalasers, tanks, and, most importantly, giant flying airships, and what are we doing? Trudging along on the ground in Orr, escorting dolyaks, setting up supply camps, and rooting out the Risen, nearly all of whom have the distinct disadvantage of being unable to fly. Sure, there are Risen Eagles and Risen Knights, and Big Z himself, but the rank and file of the Risen army is particularly ground-based. Carpet bomb 'em all and move on.
Again, that would have made for poor drama; Guild Wars 2 isn't a bombing simulator. Epic fantasy tales and video games (which are often epic fantasy tales) often ask us to suspend our disbelief just enough so that they can tell a good story. And, a few years after Zhaitan, when the Pact did attempt the very logical course of an aerial assault against Mordremoth, it didn't go so well. At least we know Trahearne had the idea.
Evil takes root
So it makes sense that you'll have to proceed through the Maguuma Jungle on foot and fight Mordremoth and his minions in hand-to-hand (or rifle-to-tentacle) combat. But there's one other logical progression in Heart of Thorns I hope ArenaNet takes advantage of.
We've already seen in some of the trailers and gameplay footage from Heart of Thorns that sylvari are, to put it mildly, not entirely trusted by the other races. Without delving too deeply into the more unpleasant parts of history, it's not uncommon to see innocent people of the same race as the “enemy” be discriminated against or marginalized... or worse. Realistically, sylvari should suffer the same prejudices, and perhaps even outright hostility, that's occurred throughout history.
The Point of No Return cinematic hints at possible armed conflict between sylvari and the other races, and fights against Mordremoth-influenced NPC sylvari could be possible. But how would PC sylvari feel about this sort of thing, and would there be a way to approximate some kind of anti-sylvari sentiment that goes beyond just a few harsh words?
Pruning the tree
I think that's a direction ArenaNet has hinted at enough that it's bound to be presented in Heart of Thorns, but as cool as it might sound, I'm having a hard time imagining how it could be properly implemented. You can't just have four-races-versus-one open-world PvP, for obvious reasons. Even a kind of limited PvP – like, maybe a sylvari can temporarily channel the power of Mordremoth and be strong enough to take on four comers in a fixed battle instance – has its issues. First, people who don't like PvP would shy away from it. Second, while just about everyone probably has a max-level sylvari at this point, would it still seem exclusionary to those who don't, or who just don't want to play one? And while it might make for a cool one-off encounter, if four non-sylvari beat a sylvari who just “Mordied up” into submission, why would they let that sylvari live (see: Scarlet Briar, Aerin)? Maybe it could be a kind of “training scenario”?
Another thought, though... there are dragon minions of all races (minus sylvari): Risen humans, Icebrood norn, Branded charr, and so on. Yet we haven't seen Mordrem asura or the like – not yet, anyway. Sure, sylvari are especially vulnerable to Mordremoth's influence, but there's no reason to think that the other four races are immune once Mordy gets his tentacles in them. Perhaps all races could be susceptible to being Mordremized, and the battles we're seeing hints of aren't “evil sylvari” versus “good non-sylvari” but sylvari versus Mordrem minions. Once the other races see how their own can also be perverted to serve the dragon, racism against the sylvari won't be quite as pronounced. And, of course, the search for a cure would be a major storyline...
There are a lot of directions ArenaNet could go with the anti-sylvari “movement,” and I hope it's not simply glossed over because it would be uncomfortable or difficult to implement. Like the eagles-to-Mount-Doom plan, it's too obvious to be ignored, and it's a chance to tell a great story, one that's not about swords and spells but about fear and distrust – which can cause more damage than an entire horde of dragon minions.