I already own a sizable Slaanesh Daemon force that has been sitting on the shelf since shortly after the last book was released. I hated the random deployment in the last codex and as such I played a grand total of three games with them before putting them back on the shelf. Initially I picked most of these models up to accompany my 3rd edition Emperor's Children marines. Who along with all my other chaos marine stuff has long since moved on to another owner, as it seems GW has no plans on bringing the army anywhere near what it was when I enjoyed playing them. However I held onto the Daemons as I enjoy the look of the Slaanesh models and figure they'll look nice on my shelf if I ever finish painting them.
At first blush it seems the new Daemon Codex is a huge improvement over the last book, contrary to what the rest of the internet tells you. It seems that a full Slaanesh force is a viable option, and I plan on building out a few list options using the models I already own. I still am trying not to sink any more money into 40K models until I finish eveything I have in the que, so I'm not looking into any of the new models yet.
A while back I picked up an Ultraforge Pleasure Demon, I just liked the model and didn't really have any plans for it (plus it was on a clearance sale at the time), so it sat on my shelf partially assembled. Reading through the new book I really think I should use a Blood Thirster in my list, problem is I hate how the Khorne models look and in general the asthetic of the daemon book bothers me. When you run a mixed force the models don't match up and look like a rainbow vomited on the table. (Chaotic sure, but ugly as hell) So my solution is to use the Ultraforge Demon as a Blood Luster of Slaanesh, it solves my problem of fitting the look and feel of the rest of the force while allowing me to use the rules for a model that I think is fairly strong.
I'm going to try out a all Slaanesh list a few times to see how that works out and if I like playing them I'll finish up the army. (adding yet another 40K army to my que) And if I really want to add some of the other units I'll probably just scratch build some stuff (maybe I'll be able to use those Soul Drinker bitz after all ... Sarpedon might make a decent Herald on a Chariot, an a unit of mutated marines might pass as flamers or horrors).
My initial thoughts are: 1x Bloodthirster, 1x Keeper of Secrets, 4x Units of 12 Daemonettes (2 with banners), 1x unit of 6 Steeds, 1x Slaanesh Daemon Prince with Wings, 2x SoulGrinder w/ Phlegm. This comes in just under 1500 points and puts 59 models on the table. I have a feeling splurging on the random gifts might be useful however for my first run through I don't want to spend points on upgrades.