Well, consider the Kill-Marines dropped, but I still think something like them would add an interesting element to the Hellhounds.
I've had a think about Griven Kall's personality and appearance. His up-bringing has left him paranoid about betrayal, and quite jaded. He's generally pragmatic, and is willing to do what needs to be, other than dealing with xenos and traitors.
Kall is bald with a few scars, and wears relatively plain clothes when not in his armour.
Hey Gulag, here's my ideas on the Hellhounds, so far.
Griven Kall grows up on a world (currently unnamed) where various xenos races wage war against each other, and the local humans. Eventually Kall agrees to an alliance with one of the xenos races (also currently has no set name), which turns out to be a bad choice, as after a while the xenos enslave the humans. After defeating the xenos, Kall declares that never again will he trust a xenos, then begins an aggressive campaign against all the other local xenos, scavenging their tech to use against them. What everyone has been fighting is ancient technology of unknown origin, which will only be hinted at. After the finds him, Kall calls his Legion to his homeworld to cleanse it of the xenos once and for all, which would leave the Hellhounds with a great sense of unity.
They are follow the standard Legion organization, with the addition of the xeno-tech specialists Kill-Marines (look up Deathwatch Kill marines), who often act as infiltrators.
I don't have too many ideas for the combat doctrine at this stage, other the Kill-Marines infiltrating, and the Legion otherwise mostly preferring direct tactics
They believe that no xenos can be trusted, so that they can't betray them later.
That's pretty much all so far.
Perhaps it would even be possible to come up with actual TT rules for Twisthammer Legions/successors, both pre-Heresy and post-Heresy. I would be quite interested to take part in that, especially since I will have some availability now.
I would love to go back to that, perhaps finish up the Primarch write-ups, do a brief summary of the Heresy, its aftermath, and state of the galaxy in M41. I am posting up "Reaper's War" on The Bolthole forum, and reading through it made me realize that Twisthammer-verse was a great idea, worthy of more development and time.
Speaking of Twisthammer, would you be interested in resurrecting it? I was thinking the original Twisthammer (the world of "Reaper's War" and twenty quirky and mostly reprehensible Primarchs). What do you think?