An enterprising internet denizen has guessed that Kratos' brother will appear in God Of War 3, possibly as a villain.
In the first God of War, there was a video which was played after finishing the game on any difficulty, explaining the origins of Kratos as a child of Sparta and that his brother was abandoned in the mountains for being too weak to be trained as a fighter. The brother came of age in Hades and is out for revenge against Kratos for leaving him to die. The God of War Collection released in November for PS3 offers a silver trophy (Legend of the Twins) for merely watching this video. Playstation 3 Center has surmised that this must mean that Kratos' possibly demonic brother will appear in the next God of War game.
While it's not completely far fetched that this might indeed point to the content in God of War 3, which is due out in March, it seems a little bit of a stretch that this is a deliberate hint from the developers. On the other hand, games have had much more elaborate marketing campaigns of late (Dante's *cough* Inferno.)
Perhaps publishers seeding of viral content like this is the next step in the battle to get big dumb journalists to write about their next game.
Hey, wait a minute...
Source: PS3 Center