Anyone and their mother knows that EVERYONE will be going to Silvermoon to defend the Sunwell, even Void Elves. And early leaks confirm Alleria will earn the title “Ranger-General.” We don’t yet know if this means of the Ren’dorei or Sin’dorei, but let me back up a moment and explain why this works so well.
Thematically, the Light and the Void are at odds. It is no joke to say that, with the Sunwell being powered by the Light, the Blood Elves represent it. Meanwhile, the Void Elves represent, obviously, the Void. Remember this.
Alleria, and every Void Elf like her, were banned from Silvermoon for how their pursuits in harnessing the Void posed a threat to the Sunwell. After Umbric’s Blood Elves were exiled and mutated, they also recruited High Elf Wayfarers and even a few Darkfallen. Essentially, they are the outcasts of Thalassian society.
Another point before I drive this home. Metzen previously announced the Light and the Void would clash, but not all would go to plan. Things would go wildly out of control. And then the Titans would return to Azeroth. All of this started to reveal… a theory.
Using Blood Elves and Void Elves as analogies, let’s think about this. What if the Light and the Void are not mortal enemies. What if there is something larger than them they will need to team up to face? The Void Elves will be at Silvermoon, fighting back the Void alongside their Blood Elven brethren. What if they defeat the Void, but an even greater threat emerges? And what is left of the Void will need to team up with the Light?
I could be going off the rails with this. But it’s entirely possible Void Elves could defeat the Void and, the Void no longer being a threat, the Ren’dorei could be allowed within Silvermoon permanently. Could this be a hint of things to come? 
Much to ponder.