Most of the images are taken off Google to give a visual aid to the untis, and to keep this from being one giant wall of text.
To keep things simple, lets start with the Army wide rules and Core units. So my two cents...
The two rules that come to mind are the Chaos Marks and the Eye of the Gods.
Starting With Marks, I like to see what abilities they would bestow. I have been in the game since late 6th eddition, so I have gone through 3 Dark Elf Books (Plus or Minus 2 Cities of Cigmar books).
From what I remember: For a couple more points per mini (10 to 15 depending on mark for monsters and charecters).
Chaos Undivided, no frills standard.
Khorn: I am Thinking The Only Thing They Fear is You for theme music. I suspect this mark will make you Frenzied. I wonder if it will add anything to anti magic. We know magic will be 2 dice per spell, so no need to have a Power and Dispell Dice pools. Shame, as I actually like the idea of 6th ed Khorn granting +1 Dispell DIe per unit with the mark. Overkill, but I also want to see some strong anti magic here with this guy.
Slannesh: Not Sure If I should have Bloodhound Gange's Bad Touch in the back of my head with this one, or Because I got High. I suspect The Dark Prince Will grant Immunity to most of the Psychology, and might just have Immune to Psychology to save on space. Other units like spawn and GIants had move movement.
Nurgle: Time for the Pusle of the Magots with this one. 6th eddition he made things have fear, and if the monster already had it +1 toughness. Later on it was a -1 to hit due to trying to find a hit on them with all the flies and the bad miasma. Regardless, I want this mark to keep Nurgle being the Anvil to Khorn's hammer.
Tzeentch: Not sure for theme music, something macavaelian. Maybe When Your're Evil. The last couple editions game units 6+ ward save that could be combined with others. I was never sure about this as it made it seem a little...odd. IDK, it just didn't fit. But we won't see 6th eddition everyone with the mark Grants an Additional Power Die. But haveing none sorcerers take spell levels might be fun, and sorcerers getting better perks to casting. While Khron will mostly be anti magic, this is all about it.
The other main army rule that will be interesting to see what they do with was Eye of the Gods. If I recall, when a champion or character kills another character or champion in a duel, or got the killing blow on a monster they could roll 2D6 on this. The result usually meant a stat increase such as WS or Strength. It could be nothing, it could also be improved armor. Or you could roll a Double 6 and get an awesome ward save with a chance to become a Daemon Prince if you have the mini. (so even if you don't plan on fielding one have one on hand just in case). On the other hand a double 1 gives you stupid and a chance to become a chaos spawn, and also have of those just in case. It will be interesting to see what this looks like.
As for units:
Core
Marauders
Marauder Horsemen
Warriors of Chaos
Chariots of Chaos
Warhounds of Chaos
Forsaken
Marauders: Normal humans (well, at least by Chaos Standards). Aside from a WS 4, they are not much different from say an Empire State trooper. They can take marks, a full command, and should come in cheap. Even when you add marks, and weapon options (great weapons, flails, hand weapon, and I think duel wielding hand weapons, and hand weapon and shield). If they have a weakness, being a chaos unit they will have a far larger base than most units, and unless they take a shield, will only have light armor to deal with. So shooting is a very good option when dealing with them. Aside from that, for point cost there isn't much that is bad about them, but not much that goes above and beyond the call of duty.
Marauder Horsemen: If I think an average Marauder will set you back 6 points naked, these guys 14 or 15. They can take spears or flails, and they can take throwing axes or javelins. Command options. They can take marks and full command options. They are fast cavalry, but only if you take light armor or a shield (not both). At which point they just become...cavalry.
As fast cavalry, they will have the strengths and weaknesses associated. That said, their speed and maneuverability should make them good with either rear charging, flank charging, or bypassing the stronger enemy units and go strait to the shooting units like archers or bolt thrower crews. But being lightly armed and armored, they can't handle most stronger units unless they are supporting a stronger unit.
Warriors of Chaos: The namesake of the army and what D&D anti paladins wish they were. They get in close combat and they are your units, you win. They are the one you are faceing? You die. Ok, over exageration but by how much? A point short on attacks and Wounds aside, a mini from this unit would be a hero in any other army. They have Chaos Armor, which has a 4+ armor save, and can take a sheild, an extra hand weapon, halberd, or a great weapon. Maybe flails this time. High WS, good Strength and touchness, good armor, and high number of attacks standard, makes them pretty much close combat blenders. Add things like the marks and the weapons makes this worse. I think they could take magic banners, not sure if its just 25 point ones or up to 50 points.
Their main down side is they will be pricier maybe 14 or 15 points each, which goes up when you add marks and weapons. Soo you probably won't see lots of them. That said a block of 15 to 20 is just perfect for them to kick ass and take names.
How to deal with them: Whittle them down. Range attacks that ignore or reduce armor are going to be a must. This usually means war machines like bolt throwers (if if another army, stone throwers and cannons), and firearms like handguns. Anything to weaken them with hexes, namely their armor, WS, and S, and T to even things out also a must.
In melee, great weapons and killing blow will do wonders, and lets face it Executioners are hands down one of the best if not THEE best unit Dark Elves have. We'll wait and see what magic banners are available, but Executioners with a banner that gives them extra armor penetration, and good times. Depending on what they are armed with, it dosn't have to be much. A Reaper doing multi shot can go through at least 2 layers of armor if I remember right, and that would reduce most chaos armor to a 6+ save (5+ if they have shields). I also suspect the Lore of Metal will be your best friend with them.
Chariots of Chaos: Maybe a 100 points a pop. I wonder if they can come in units of more than one like in Age of Sigmar or just one like they did in ye olden times. Either way, their may draw is on the charge they cause at least D6 impact hits, with scythed wheals probably granting an extra hit or more strength to the damage caused (different editions had one or the other). Their main draw back is they could not march in older editions, and wide flanks, and if the dice gods were displeased with you could role low on how many impact hits they get.
That said, because of a movement of 8 or 7, I think they would be good units to support infantry. Have this get the charge in, then have a nearby unit of Warriors of Chaos get the flank, or this takes the flank and the other unit gets the front.
Warhounds of Chaos: Puppers of chaos. WHat they lack in LD and most abilities to handle most strait fights, they make up for in high maneuverability. Like with the Horsmen, except half the price, they can get a flank, or skip the main engagement and get the far weaker shooty units in the back. Like Fast Cavalry, they seem tailored made for chasing fleeing units. That said, while I think poison is a great upgrae, the 6+ AC take if you have points to spare. THey probably won't take down a Bartonian knight on their own, but they can help out some.
Forsaken: What happens when a follower of chaos gets more "gifts" of the dark gods than they can handle. They loose their mind, becoming frothing mad animals with little sense to their identy or their origional quest to glory; only death or spawndome lie ahead for them. They got models in 8th edition, but I can see this being a kit bashing dream.
I might get some Mauraders just to put some spare parts togeather to make some forsaken.
When they first came out in 7th edition they have heavy armor (their bodies making it buckle and fall apart) but 8th edition gave them chaos armor. They had a random attack of D3+1 so any given round of combat gave them 2 to 4 attacks ( so a rank of 5 would have 10 to 20 attacks). And they were frenzies. Different marks gave them different things like Hatred, Improved Speed, Poison attacks, or magical attacks, so it will be interesting to see what they get. 8th eddition also have them a panel you had to roll on to see what their random mutations were which could be good or bad depending if the roll was closer to a 1 or a 6. They were a little more expensive than Chaos Warriors, but they had alot of the same states and some better base attacks. I don't see why not take them if you feild this armor.
As for how to deal with them, same as warriors. Because they are frenzied, you could try distracting them with a small unit of Fast Cavalry with at least a musician in the mix so they get up close, flee, then rally the next turn to do it all again.
Your thoughts, strategies, or things I missed? And would you take any of them?
I can see Warhounds being taken, say in a Karon Kar Heavy list. And who dosn't want warriors. Forsaken, I might take for flavor reasons.