Been thinking about the Chaos Legions recently. The majority of the 40k background material suggests that the Chaos Space Marines who live within the warp are the 10,000 year old survivors of the Horus Heresy, kept alive either by the dark power of the Chaos powers, or by the strange shifting of time within the warp.
But there are also tantalising suggestions that some Legions are still recruiting. The Alpha Legion write-up in an old WD suggests that they recruit many of their marines from within the Imperium itself. Other Chapters - notably the Night Lords - are said to have extremely pure geneseed that remains relatively untainted by the warp, suggesting they're doing something with that same geneseed.
I think it's too simplistic to say that even among the more tainted and" chaotic" of the chaos legions (Death Guard, Emperor's Children etc) that ALL of the members of those legions are the same individuals who rebelled against the Emperor. Sure, many might be. But I am interested in the idea that perhaps a significant proportion of the Chaos Legions are new recruits, humans from warp-trapped worlds, renegades or the offspring of slaves bred just to provide recruits for the Chaos Legions.
I also like the roleplay potential this creates: a Horus-Heresy era chaos marine might have a very different outlook on the universe to a more recent recruit. A more recent recruit might regard the Heresy-era marine as a loser, a tired old warhorse full of tedious stories about an ancient war, and embittered about his defeat.
What's your take on this? Personally, I think there's a great deal of room for Black Crusade to explore precisely what the Chaos Legions have been up to for the past 10,000 years within their strongholds.