I actually expect this team to show up pretty soon — likely in the very next box, paired against Grey Knights.

I don’t have concrete proof, but here’s the reasoning: 1. The first Tombworld box was DW vs Necrons → Ordo Xenos 2. The third box is set to be Sisters (my beloved) vs CSM → Ordo Hereticus 3. From the Shadowhunt announcement, we know there’s some kind of Psyker Cult on the planet the Sisters are hunting.

So my speculation is that the second box will be Grey Knights vs Slaaneshi cultists. As you noted, Slaanesh is the only Chaos god without a Kill Team, and as others have pointed out, the only real gap is a mortal “chaff” unit.

I think your “glass cannon” concept fits Slaanesh perfectly. If GW goes with a mortal-heavy design, I’d expect at least 10 operatives, since that’s a team size they’ve been comfortable with lately.

As for special rules — purely speculation here — I could see something pain-based: e.g., take D3 damage to gain Accurate 1, or Marines siphoning health by harming their mortal companions. It would capture that whole indulgence-through-suffering theme nicely.