Its been years since we have seen the Traitor Legions in Warhammer 40k, all the way back to 3rd edition White Dwarf or Chapter Approved rules. Back then fielding the Iron Warriors, Night Lords, the Emperor's Children were all quite common. The battle between Chaos Marine Legions and Space Marines is an iconic part of the game.
Right now the Traitor Legions in 40k are barely more than the color you paint your models according to the rules. If you want to properly play with them, you have to invest into the Horus Heresy from Forgeworld, which is not a bad thing, but its still not the standard Warhammer 40k game that you take to league night, or to local tournaments, or even the occasional pick up game.
Don't get me wrong, Forgeworld has done wonders with the Traitor Legions, and the models released along with the upgrades packs are nice. They supplement the 40k player with new shoulder pads, etc to really characterize your chosen Chaos Legion. It is however a lot of neglect, that the most iconic conflict in the game, is left to the Horus Heresy, and not handled in 40k.
Games Workshop has danced around the issue for years. The Crimson Slaughter release was all but a, "We are not going to do the legions any more", "We are leaving the Traitor Legions to Forgeworld". Yet is there not a larger audience for each of the legions than there is for Harlequins? Releasing the Legions would feed not only Forgeworld as players went there for some extra shoulder pads etc, but it would revitalize the Chaos Marines for 40k. I would argue that a lot of the discontent from Chaos Marine players does not come from the game play of the codex, but from the fact that they feel left in the dust with each release, and their legions ignored and reduced to a paint scheme.
The Black Legion supplement was as step in the right direction, but it seems that all went quiet soon afterwards about future supplements.
Chaos Space Marines in Warhammer 40,000 offer such a rich and diverse enemy of the Imperium, that I am surprised we have not seen more dedicated to it. Are the Chaos Legions reduced to such small, scattered, and insignificant warbands that they are no longer really a threat to the Imperium? Reading their background in the current rulebooks you would think not.
I think its time to stop dancing around the subject GW, and really dig into the iconic bad guy in the 40k universe. No more miscellaneous warbands, no standard codex release, no more messing around. Lets dig in and really do something wonderful with Chaos Space Marines in the 40k universe.
The Traitor Legions
III Emperor's Children Traitor (Slaanesh)
IV Iron Warriors Traitor (Chaos Undivided)
VIII Night Lords Traitor (Chaos Undivided)
XII World Eaters Traitor (Khorne)
XIV Death Guard Traitor (Nurgle)
XV Thousand Sons Traitor (Tzeentch)
XVI Black Legion Traitor (Chaos Undivided)
XVII Word Bearers Traitor (Chaos Undivided)
XX Alpha Legion Traitor (Chaos Undivided), possibly still Loyal