Excuse me, but I do better controlling my urges than most... I swear.

But I would love to see either the Crimson Fists or the Imperial Fists there as well, or any other Chapter that is not presented much in general, for example the Iron Fists or the White Scars, etc.

I just simply named the three chapters I would most likely give my vote to, IF I can only vote once!

Crimson Fists! Their story is just awesome. On the brink of being wiped out. Trying to regain strength again of a full chapter. With Pedro leading them.

Oh yeah, there's a ton of fringe (less popular) chapters I'd love to see:

Howling Griffons, Red Scorpions, Iron Snakes, Raptors, Mantis Warriors, Death Spectres, Sons of Medusa... just to name a few.

Probably gotta get through the First Founding Legions/Chapters and Black Templars before we see anything else.

Well, i'm assuming that chaos will have Daemons of some kind, so i thought we would be able to get Grey Knights in some form. Seeing as the biggest difference between CSM. and 'normal' SM is that they can use Daemons and magic. I don't see why they wouldn't be able to use, for example, a Bloodletter etc. So i was thinking Grey Knights could be used to counter Daemons, but do worse against other enemies.

Though, i would be fine with Deathwatch in instead of GK.

I suppose that could work, it's just the issue with their role/OPness vs. everything else. You could nerf them some way against non-daemons or chaos, but that would feel kind of contrived.

Technically SM and CSM both use "magic" ...They are just used and named differently.

and besides, Grey Knights may be anti-daemon specialists, but I don't see a Space Marine completely helpless against a Daemon. Especially if they close the Warp Portal allowing said Daemon an anchor into reality.

I would not recommend adding Grey Knights to the game... they are quite OP even in the Lore. To balance that out, the CSM would at the very least can only use Daemons in some limited way.

Yea that is an issue, but maybe they can make it so they can only be spawned after, let's say a Greater Daemon is summoned, or something along those lines.

Maybe they could have a home fortress of sorts for the 4 races, that is your foothold on the world and if you lose it you are pushed off the world and you have to start over. (Like DoW.) So let's say chaos is defending agents SM, chaos get's to summon a Greater Demon and some lesser Demons to help the defense, but SM get to spawn a very limited number of Grey Knights to counter this.

That's at least two votes for the Salamanders then
Looking around at the popularity, I think the Black Templars or Imperial Fists would be the favorite to be implemented next though?

Salamanders are an amazing Chapter, love everything about them. The reason I chose Imperial Fists and think they would work well in game is because the Iron Warriors are supposed to be one of the playable armies for Chaos. Everyone knows that the Iron Warriors and Imperial fists have a huge grudge, it would be fantastic if small story stuff could be built around lore like this and make players feel the hatred for each other.

Plus, it would be a long fun battle if the Imperial Fists/Iron Warriors had a siege vs siege scenario going