So for a slaneesh demon army using the “skull cannon” rules but wanting to stick with the slaneesh feel, what about a “booby” style demon strapped into a stirrup examination table with something (havent decided on cannonball, skull, demon head etc) flying out of her/its you know what…??
It’s your army, your models, your money, and there is nobody in the world telling you what you can/cannot do to your miniatures. Whether it would be appropriate or not… that’s a different matter. I doubt you’d get much support in your friendly local Games Workshop - they tend to be quite family friendly after all. There’d be other ways to represent Slaaneshi warmachines if you wanted the GW seal of approval - something sinuous, yes, something beguiling, curved and lithe and all those things, without being so ‘in your face’, so to speak.
That said, if you’re intent on it, have a look at some of the Slaanesh soulgrinder conversions around; they might give you some ideas.
Funny thing is it doesn’t seem that odd to me. I started playing in the late 80s early 90s and all the Slaaneshi units were like this. The art was all like this, etc.
That’s to say nothing of the weirdness of the late 70s early 80s before my time which were very weird.