Watching the Twitch Channel for Warhammer in the week, there were plenty of previews coming out of Forge World. These not only included the miniatures (Astraeus, Red Scorpion chapter dreadnought, space wolves terminators, doors for rhinos, etc.), but also a quick glance through the new rulebook for the Horus Heresy era.
Described as Version 7.1 of the rulebook, on screen it appeared as a large tome held together by a pair of large bulldog clips. In other words -- a high level proof. All the pages were printed and ready. Everything was there. Just the binding missing.
The guys explained that the rule book has been sent to the printers and they are estimating something like one month or so before the book is ready.
I'm still pleased that the Horus Heresy will be adopting a modified 7th edition, but sad that it is not wholly compatible with 8th edition (meaning one set of rules for 30k, one for 40k). I guess I will withhold judgement until I can actually get my hands on the new rulebook to see what has changed. Exciting times ahead!