Today on the heresy show, we learn how to make good fluff!
Okay, we will need:
A massive rebellion named after someone called Horus.
Okay, let's get cooking!
First we place the Emperor into our cooking bowl, don't worry about being dainty with him, he can handle it (Unless you're an Ork Warboss >_>).
We then place the Warmaster into a separate bowl. Remember, this is important. We then add heresy into the bowl and BAM!
We have our Massive rebellion (I may have lied about you needing that one earlier on).
Anyway, so now we simply add the two bowls together, add a sprinkle of life, a dash of death and essentially, that is what the current situation is and always will be.
Unless, of course, you added the Internet.
You really shouldn't have done that.
TLDR; The storyline won't be progressing. Be happy with the black library fiction and the smaller stories of the Night Lords, the Imperial Guard, the Ultramarines, the Iron Warriors, etc. It's all about the small things that are happening now, more than the Emperor. Honestly, I think they're just trying to avoid him and flesh out smaller players.
I'm ok with that for now though, just as long as I get my Night Lords fluff books...