Cross-posted from the RWBY Wiki:
This is my own overall prediction (given our current state of knowledge) as to what might happen in the show:
Once, long ago, in a land far, far away...
The Rainbow Empire had long been peaceful and prosperous. Although once, the Whites, masters of magic and technology, had been aggressive imperialists, centuries of close co-opoeration had forged a society where the four races of the Empire each flled a particular role to the point where 'race' and 'caste' had become interchangable.
The Whites were the priestly/scientific class. Although they frequently filled govenrmental positions, it was hardly a prerequisite. However, it was the Whites who had developed the magic and magi-tech that made the Empire prosperous and secure. Many Whites, using their ice/water-elemental magic, were also great healers;
The Yellows were the warrior caste, using their fire-elemental powers to rain destruction on the Empire's enemies, both internal and external;
The Reds were the agricultural caste, using their kinship with all things alive to feed the millions of citizens of the Empire;
The Blacks were the worker caste, using the might that came from their rock-elemental magic to drive the mighty factories, mines and foundries from which the iron backbone of the Empire was forged.
However, in any society, there are always the dissenters. A rebellion is brewing amongst disaffected members of the Red Tribes and Black Nation, chafing at their seemingly-menial status. It is a rebellion given greater strength by rumours of a girl who is the last descendent of the blood of the Kings of the Black: the Beautiful Lady of the Black.
In recent years, life in the Empire seem to be growing darker. The Emperor Kalter Schnee, once a kindly and beloved monarch, is increasingly cruel, cold and distant, an affliction blamed on the death of his young wife. There are those who also grumble that his second wife, the ambitious Black Nation crystalmancer and oligarch Maelia, has been twisting the old man's soul. Certainly, eyebrows were raised at his decree that Maelia's two daughters (by her own first marriage) should be considered to succeed him before the child of his first marriage, the beautiful (and musically gifted) but perpetually sad Weiss.
Weiss's power and talent is far greater than any Princess of the White before her. Because of this, in an unprecedented move, the Emperor has decided that Weiss should attend the Institute of Gifted Children to learn to harness her skills fully. There she has been joined by Blake, a mysterious girl of the Black Nation, whose eyes are filled with sadness and anger, Yang, a happy-go-lucky girl of the Yellow War Bands, who is determined to be true to the oath every one of her people have sworn to defend the Empire and its people and finally by a small girl named Ruby... a girl of the Red Tribes with a gift not seen in generations... the last of a lost order of mages and warriors, sworn to maintain the balance of the nations.
Together, these four must learn to overcome the prejudices and fears of their respective upbringings and work together. For there are worse things in this world than gangs of school bullies and unprofessional tutors. A dark shadow is falling over the Rainbow Empire, a shadow that threatens to smother all four races in an eternity of tyranny. A shadow with a name that is whispered where-ever there is darkness in the hearts of men's souls:
This is the story of how four schoolgirls from the most different backgrounds became the champions of all the peoples and the bearers and protectors of a fast-fading light.
This is the story of RWBY.