Well it will be interesting to see what happens to the Blood Angels.
That White Scars idea would be great, because Khan did have to make a momentous decision, and that decision could have changed the outcome of the Heresy one way or the other, and that sort of decision making is what good books is all about.
Saying that it wouldn't have been a hard decision for Khan is just robbing him of his humanity and all emotion, and we're always moaning that space marine novels brush over the humanity and emotions of their protagonists. Does Khan help is brother, or his father? That's always a hard choice to make whoever you are.
And we forget that Alpharius is his brother too, so that makes the decision even harder. This story would also help shed some light on the relationships between Khan, Russ, Dorn and Alpharius.