Slaanesh based Chosen.

[Tesq]

All appereancs you see in ic are tzeench one re colored for slaanesh. Yes there are cultist and chosen stuff but is limited to Lost vale stuff unless they can dig something cool out of the client database.

[tazdingo]

grimnir said that client control would allow custom assets. time to attempt to learn blender for the 80th time...

[Gravord]

Adding Slaanesh chosen would take a lot of work, including new animations not existing in game. From gameplay perspective Slaanesh would have strong and annoying dots - as a means to inflict long suffering and painfull death. Other chosen abilities would be aoe ground snare (hands coming out of the ground to grab and tickle people passing by) and clouds of alluring toxic scent distracting targets (and inflicting cd or cast time increase).
Could be done, could be good tank or dot based off tank but the amount of work would be enormous.