An Alliance cinematic would be hard to do in terms of equitable representation. In the game Saurfang is mostly absent while other Horde characters have their own segments shown during gameplay. For the Alliance it would be hard to do the same, since Blizz benched most of the characters. To have an equivalent cinematic for the Alliance, Blizzard would need to show a similar focus on an iconic character whose voice can't be heard in game. When they decided to write off the NEs/Gnomes, that left no one else to take the mantel but Genn, Jaina, and Anduin. Problem is that they're already so prominent in BfA that it would be redundant to give them (especially Jaina) more screen time. There is no proper Saurfang equivalent. The Alliance needs its prima donna.