Chaos Dwarves vs. Ogres or die, plx?
On a more serious note, I can see the point of having Chaos vs. Brets/Empire, but something tells me Empire is more likely. Empire provides a player with a variety of stuff instead of just the Knight Rush, making it a far better set. I can also see perhaps some sort of gimmicky 'Second Wave' Chaos unit - such as Forsaken, or FB Spawn - released much as Nobz were for Black Reach. That would be awesome - the rising alongside the fallen.
On the other hand, why not Beasts of Chaos vs. Wood Elves or something? Both not included in a starter set before, narrative enemies much like Dwarves/Goblins, and at least ONE of them is likely to have an army book before new edition hits if the WD spoiler is to be trusted. Both ranges could use the sales growth as well, right?