Don't you guys think that if they were going to make a Darkoath faction they would have given the Darkoath Warqueen a "Darkoath" keyword?
Also, slaves to darkness has so many models, but no battletome. You think they would do a release for a subfaction of that and leave StD in the dust? No way.
If anything, STD gets a battletome and some models. They can all be "Darkoath" themed maybe.