Not sure how real these are, given that these releases are a fair bit away, but;
It appears we are getting another duology in the same vein as A Thousand Sons and Prospero Burns, this time focusing on Calth; specifically, I think, the Underworld War along with the Ultramarines and the Word Bearers. If this is so then I quite welcome this, and the author choices; Rob Sanders A Deeper Darkness was brilliant and showed he can write the Ultramarines not only in a likeable fashion but also avoiding the cookie-cutter style that they can fall into in the hands of a lesser author, and David Annandale proved in The Traveller and Damnation of Pythos that he can really make the Warp scary (something few authors try anymore) and I look forward to seeing what he can do with an entire Legion of creepy and bloodthirsty fanatics.
Release dates, according to Amazon, are April 12th 2016 for The Honoured and May 10th 2016 for The Unburdened. Since that is for the paperback release, subtract a few months for the hardback version, and I think we may be looking at both of these in December at the earliest.
Edit: Sadly however it appears both of these are not true novels, clocking in at 240 pages. So we are getting a larger-novella duology, still it beats nothing I guess. But if the Heresy is going bite-sized as 40k novels seem to, then I may just be done with Black Library.