Since I am partial to mages, I'd really like to see mages get more prominent showcasing in one of those videos. As for who, either Jaina Proudmore or Khadgar.
One of the nicest parts of the last cinematic is that while so many previous warcraft cinematics focus on the mundane martial swordfighting with the primary characters, this one showcased the otherworldly powers of the banshee queen, and the divine powers of anduin mass ressing his allies in a feat of power calling holy energies down from the heavens.
It was a brilliant display of power, fantastical high fantasy elements that are beyond the kind of mundane sword and board you typically see. And frankly, the biggest examples of those kinds of showcases, are mages themselves.
The closest we have gotten are brief sequences like that mage atop the tower blasting the infernal, casting sheep, that kind of thing, but not a main character engaging in one powerful feat of strength/power. That would be great to see for even more classes, and I'd choose the mage to be featured.