I totally agree with both posts above (especially @MossyToes, because Chaos is what I play and principally interested in since my come-back into the scene, but Space Marines are the ones I played before - Angels of Death and Ultramarines Codices of the 2nd Edition - and I therefore quite understand the lack of characters for other chapters than the Ultramarines).
The 5 things I think necessary to change regarding Chaos (mainly CSM, but with some close links to Daemons) are :
- The standardisation of the "Daemon" trait : the same wording and advantages for "Daemon" (CSM), "Daemonic Possession" (CSM), "Daemonforge" (CSM) and "Daemon of ..." (Daemons), including all of them being "Fearless" and replacing the "Ignore crew shaken" with the invulnerable save for vehicles (personnally, I would add "Eternal Warrior" to Greater Daemons and Daemon Princes only, but maybe give 2 Wounds for models which are hosting a daemon, like Possessed, Warp Talons, ...). And the possibility to buy "Daemonic Possession" on a Helbrute (just a detail compared to the rest, though).
- Lowering randomness : Chaos is entropy, and I'm not discussing it. But, even then, CSM and Daemons Codices play too much upon it compared to other armies (dice rolls for activating an artefact, for chaos boons, possessed advantage for the current turn, ...). That (too often) makes us roll dice to gain not-so-great-assets-compared-to-other-armies while taking the risk of seeing what has been paid for (and, sometimes, not for a cheap price) not only be unuseful, but also work against us. Paying so much for a possible +2 invul to one unit per turn with 1/3 chances to give it -1, or (amongst others) removing scatter for DS reserves only after CC kills are just a waste.
- Improving assault : Chaos is a CC oriented faction, but lacks of basic assault advantages, in matters like "offensive grenades" (Possessed, Warp Talons, Mutilators) and vehicles (just one, and an expensive one, for an assault oriented faction is not much enough). This can be done by adding Stormraven or Drop Pods equivalents, considering Rhinos as open-topped, ... and allowing CSM hosting a Daemon to keep their basic gear, for instance.
- Developing characters : some standard profiles (like the Dark Apostle or the Warpsmith) are far too limited to really be useful (except in very specific army lists). For named characters, the issue is basically the same as for Space Marines : a lot of them are missing (from the fluff or even from some profiles in the rules - talking about a named Dark Apostle with specific gear or abilities, for instance). Some of them, like Abaddon, should also be raised to Lords of War.
- And, finally, diversifying Chosen : these are supposed to be the elite (both into the fluff and the game) of a Legion/Warband, and they are limited to special weapons and a rhino. They should have access to different abilities and gear (jump packs, infiltration, tank hunters, daemons, ...).
I don't know whether GW is planning to provide us with a new version of the CSM Codex (it's probably not a waste to invest into CSM for a brand new release in a 2 or 3 years term), but it also seems useful to handle the short term. And, within the current system, this can rather easily be done through Detachments and Formations (giving special rules for particular organizational charts without directly modifying the Codex). I have made my personal attempt on this ( https://www.heresy-online.net/forums/showthread.php?t=199002
), and I'm not the only one.
It could be a quick way for GW to patch things (not only for the CSM, even if they are amongst the few factions which have the fewest Detachments/Formations of the game) while working upon a new Codex at the mid/long term.