It is not a matter of how many people like She who Thirsts but actually representing her/him/it in a meaningful way and i think that just minor deamons are not the way especially since a few(ok more than a few) months back there was talk about a God dedication post launch.
Well then give them Emperors children, that should be enough since they are the warband that represent slanesh the best.
Yea i Noticed all of the Chaos warbands are chaos Undivided, maybe later in the game they can get some armor Like the noise marines to represent the great enemy.
You wonder how they're going to allow permanent marks or how the temporary ones work mate ? And I don't know I mean there's not the depth of character that would make RP work but I have gotten seriously invested in characters before in RvR games (as opposed to PvP). Especially where the IP is something I have a connection with. I will learn and dominate a certain playstyle or loadout just to fit with the theme, which isn't a problem as long as say when my raid/squad needs a cleric/medic I'm not opposed to stepping up. But yeah, I will learn every Slaanesh Mark inside and out (giggety) fairly early on and adapt it to the meta in the best way I can !
What if the Temporary marks represent service to a Daemon, but not the god? You'd get some of the power of being dedicated, but not as much as a full on Cult Marine with a permanent mark.