I'm trying not to be too spoileriffic in the titles, but very soon the new status quo is just going to have to be common knowledge. I figure we can hold off on this stuff until launch day, but not much longer than that.
So there you go: spoiler alert.
Varian Wrynn is dead. He died in a heroic act, but his death was horrific. After taking down a Fel Reaver on his own, allowing the airship to escape with the survivors of the Alliance forces (yourself included) but leaving him trapped in the middle of a massive swarm of demons. Slaying several felguards, he's ultimately stabbed in the back by two of them. In his last moments, Gul'dan approaches him, taunting him that he will have died for nothing. Varian faces his fate and replies that he will have died "For the Alliance." And then Gul'dan burns the High King from within with fel fire as the shattered forces of both factions retreat from this crushing defeat.
And so we arrive back in Stormwind, recovering from our own wounds. Genn sends you to take Varian's letter to his son while he pursues Sylvanas, whom he believes (as do most of the Alliance) betrayed Varian and abandoned the Alliance in the middle of the battle.
And thus we find ourselves in our current situation. Anduin Wrynn, who spend much of his boyhood as a figurehead "king" while his father was missing, has now become king once again, this time for real. There is no Bolvar Fordragon to act as regent (Bolvar of course became a very different kind of King) - he is the King of Stromwind, for good or ill.
But what about the Alliance? Varian was named "High King" during the campaign against the Horde in Pandaria, which officially gave him seniority to rule over the entire faction. But this had not always been the case. The Horde has always had this top-down structure where every member swears fealty to the Warchief - there was never any doubt that Thrall was the head honcho when WoW first came out.
But the Alliance was created as a partnership among equals. In its earliest days, it was composed of the six northern human kingdoms - Stormwind was still occupied by the Horde at that time, and Varian was a child and a king in exile. In fact, the only current member of the Alliance who was actually a member of the original Alliance of Lordaeron is actually Genn Greymane.
Stormwind does have some ancient legitimacy to rule over the other human kingdoms - though it's tenuous. Anduin Lothar traced his lineage all the way back to Thoradin, the first human king. But for whatever reason the Wrynn dynasty led Stormwind - with the Lothars as loyal allies. Still, the Alliance is incredibly different than it used to be. Its largest member when it was founded, for example, was Lordaeron, which is now home of the Forsaken. Granted, many people who survived the Scourge traveled south to live in Stormwind, but the Alliance is far less built around these ancient human kingdoms these days.
So is Anduin automatically made the new High King? While he has shown great promise as he's grown into an adult, it's a bit of a tough sell to get all the Alliance races on board. Tyrande and Velen measure their ages in the five-digit range (actually, Velen could be more for all I know.) At least Varian was considered mature for his species (I think he's supposed to be in his 40s when he dies,) but Anduin is still very young even by human standards.
Does age count, though? After all, Velen has seen prophecies of Anduin leading the army of the light against the shadow (which might not actually be the Burning Legion,) and so he's likely to think that the sooner Anduin gets leadership experience, the better.
The question, though, is whether Anduin is fit to lead the Alliance against the Legion yet. Sylvanas, for all her problems, is an experienced military commander and strategist - her conquest of Lordaeron against the Scourge and the Dreadlords shows that she can get things done. Anduin's experience in Pandaria left him nearly killed when he broke the Divine Bell.
That said, the Legion is not a typical threat. A simple military victory in which we clear them off the planet by slaying them and tearing down their fortifications is just not going to work - and it's clear that they are not going to relent this time, as they did in previous invasions.
Anduin is not a fighter, at least not in the traditional sense. He's a practitioner of the Light, and is clearly quite good at it (the recent comic saw him easily subdue and interrogate a Dreadlord.)
The Alliance has plenty of people who can command on a battlefield. But maybe the real leadership needs to be focused on something else - a real solution that will end the threat, not just beat it back. And perhaps this boy of prophecy, now king, is the one to do it.