The book is based on the 3rd battle for blackfire pass, so there is definitely no Sigmar model. I had a good chat with Talima Fox about the story, An Orc Waaagh through Blackfire Pass, With a heavy involvement of Dwarves of course Averland Empire.
Marius Leitdorf is likely to feature though in the story as he's such a great character which Talima agreed also Averland is just a stone's throw away from The Moot, So you never know there could be some Halflings in there too.
She also said as The Empire have such a good range of models, WF are likely to concentrate on large models and new characters, as they did with Tamurkhan.
the whole design team seem to be quite excited about designing stuff for dwarves in particular.
Oh and when talking about the Greenskins she mentioned Night Gobbos, forest Gobbos and of course Orcs