Mind you I have no connection with GW and don't write for Black Library but:
it was kinda a shock that such a significant part of the back story was chosen to be fleshed out as a series of novels,
Why? Ever since I've been on Heresy I've seen people wanting more on what happened during the years of the Horus Heresy. How figures like the Despoiler or Ahriman or Typhus became the figures they are; what the Imperium was like at its peak, how the Imperium could justify unleashing the wolves on Prospero.
i suppose that is also one of the reasons i feel they are stringing this out for far too long, we already know the story, the story itself is so intertwined with everything 40k , it is the very foundation of 40k, and as such cant really be changed as at some point Horus has to get slapped by the big E and Sanginus goes down like a five dollar hooker, the legions get divided up and the traitors flee into the ye of terror blah blah etc etc,
This is both true and false. We know what generally happened, that something happened to Horus and he aligned with the chaos gods, that he and three of his brothers purged their legions of those loyal to the Emperor and laid a trap on Istvaan V. We know nearly a decade went by before the traitor legions reached Terra and that in that time Prospero was destroyed, Ferrus Manus killed, Typhus caused his legion to align with Nurgle by having all the navigators in the Death Guard fleet slaughtered while in the warp, and the siege of Terra ended with the death of Horus by a mortally wounded Emperor.
We didn't know what exactly happened to Horus that caused his fall, how much of the Iron Hands, Salamanders, and Raven Guard survived the Massacre, what happened to Corax and Vulkan during the Heresy, why Guilliman, Russ, and the Lion were so waylaid during the Heresy, why the Khan remained loyal, and other things (both relavent and not relavent.)
Just to point something out, i think the heresy series has about 29 novels up to press, Terry pratchetts discworld series has 41 books , thats 12 more and he started in 1983 !! BL started HH in 2006.
Discworld is a series written by one author over the course of 32 years. Thats just over a book a year.
The Heresy series has between five and ten authors, thats about half a book per author per year. And when you consider that some of these authors have been writing other novels or have been meeting other commitments (I believe Abnett also does comics?) that number means much less in my opinion.
how the actual fuck have they managed to spin this stuff out for 9 years ???? and again with no sign of the concluding book in sight?
I think authors having other commitments is the best answer for that first bit (remember ADB was writing at least one of his Night Lord novels and Talon of Horus while also writing for the Heresy series and Abnett was unable to work on Prospero Burns for a while due to medical reasons.)
And personally I wouldn't say no end in sight; look at what we have that was previously known and whats left. Theres not all that much: the silent war, the changing of the Death Guard, Magnus making his choice, the Siege itself.
and on a related note , if the number of people who have dropped out on this forum alone is reflected in the wider audience will there come a point where the numbers of sales drops to the point where it is financially unwise to carry on the series ?
I doubt we are indicative of the wider audience, and I doubt the authors wouldn't fight to end the series if it looks like things are going to shut down. Just because some of us like to say they are milking all of us doesn't mean its 100% true.