I am thinking of the children...the Emperor's Children!
See, without the Dark Prince(ess?) the options are so ... mundane. Khorne is all murder-death-kill, blah blah blah, about as fun as a broken record. You've already got Tzeentch covered. And even if you'd tolerate the Lord of Decay and Despair's minions, I just don't truck with that sort for real-life reasons. So the fun-party, 50 Shades of Naughty, Spring-Breakers-Eternal faction it is!!!
I mean, who doesn't look forward to being rammed amid-ships by the cruiser "Sweet Transvestite" ? ;-)