I can't see it being about anything pre-GC or even pre-HH. Several authors have mentioned in passing now that the series is pushing on into the Age of Darkness, thus I can only see it being based around something post-Isstvan. Although I've been wrong once before. 
As someone said it sounds at this point like a non-Astartes based novel.
Although it is worth pointing out that aswell as Sanguinius having prophetic visions/dreams, so did Konrad Curze...
As someone said it sounds at this point like a non-Astartes based novel.
Although it is worth pointing out that aswell as Sanguinius having prophetic visions/dreams, so did Konrad Curze...