Cult Sorceress- This is of course the main part of our cult of slaanesh lists. Back in 6th, a sorceress had to be your general. I don't like putting those types of stipulations, but maybe a battalion could provide that part. I also think that having an option for a Dark pegasus would be a good option. 

Cultists- These would be your main units. These are the women/men with knives, no armour, totally devoted to slaanesh. Could provide an option for shield maybe, but I love the idea of having bonus attacks based on increments of Slaanesh's number; 6. 

Annointed- Also a throwback to Storm of Chaos. These are aelves that have been totally corrupted by chaos. They are bigger, beefier, and more like an athletic chaos lord. Also to fall back with slaaneh I like the options of having two swords or a spear that can be thrown. 

Devoted- These are like cultists that are of the warrior classes. Heavily armored. Heavy weapons. Very similar to executioners in playstyle.

Sybarite Cavalry- sybarite is defined as  a person who is self-indulgent in their fondness for sensuous luxury. This fits well with the cult of slaanesh theme. I imagine a city, Sybaris, where the entire city has been corrupted. These are elves that have been granted steeds of slaanesh. Keep them similar to hellstriders.

Bladedancers- By far my favorite idea for cult lists. These are the inbetween for Annointed and cultists. They are elves that are larger, stronger, etc. Basically the best fighters who are also extremely arrogant and prideful. I'm imagining a group of male elves who think they are the most beautiful, best, etc. Rules would reflect them fighting harder near other units to prove they are the best. 

Highborn on Corrupted Dragon- Black dragon egg taken by a cult. Prayed over. Slaanesh corrupted. I imagine a big purple dragon with scales and pale skin. (I use my converted Hordes Legion Dragon)

Effigy of Excess- Slaanesh version of cauldron of blood. Grants the 6+ save, but no increases. Can unbind, maybe cast arcane bolt. Whip others around them into a frenzy to gain +1 to hit.