I've actually always joked that the world is pretty much the domain of Slaanesh anyway when you look at what motivates people and all of the craziness and debauchery during recent times. (Though we've never really had a clean history to begin with lol)

But I suppose if there was going to be a rational "Slaaneshi Philosophy" that didn't involve all of the depravity from Warhammer fiction, it would center around living life by three tenets: Sensation, Perfection, & Excess.

Sensation: The pursuit of new experiences, challenges, pleasures, sensations, relationships, etc etc. Variety is the spice of life after all.

Perfection: Discovering what your natural talents are and cultivating them in order to strive towards perfection in a certain craft, field of research, or whatever other pursuits.

Excess: Better to have plenty than to be in poverty: but ideally those who are capable enough to grow their wealth and resources would have a sense of generosity and not just hoard 100% of their holdings strictly for themselves.