Unless I read the rules wrong, there is a movement difference, in that they can't go 12 in the movement phase, thus shortening their effective charge threat range. So while great for tau to Jump shoot jump, raptors and assault marines would prefer to get 12" closer to the enemy and be able to charge that turn. Relentless would be really situational as unless TKE makes major changes they won't be carrying more than 2 rapid fire weapons in any squad size.
I had a couple of other trait style ideas (although I do like the meltabombs and defensive grenades):
IW - to represent both siege and 'Forlorn Hope' style warfare (Storm of Iron, McNeil)
Warsmith may purchase one of two special rules (names are placeholders) "First into the breach" - squads of types X, Y, Z, receive +1 WS and +1A when they have a model within 6" of the character. A squad joined by the character also receives furious charge.
"Master of the siege" - squads of types X, Y, Z receive +1 BS and the 'tank hunters' special rule within 6" of character. A squad joined by the character also receives relentless.
I would like to receive some feedback on the above. I have great respect for you, TKE, and admire the work you are doing with this chaos codex. I just think that chaos needs some force multipliers and ability bubbles from (suitably toughened up, I hope) HQ choices that offer flexibility could be a cool idea to work with outside of the special character realm. I'm basing this on characters like the Khan and Dante who provide significant bonuses to their own units, as well was w/e the space wolf character's name is, and the presence of several "bubble" force bonuses in recent codices such as blood angels and space wolves psychic powers, the sanguinor, and pedro cantor.