Stalemates only are fun for so long though.Or Abbadon dies. Chaos actually take a blow. It doesn't have to be the Imperium that takes a blow. Maybe subtle changes on all sides. This doesn't really need to happen though as stated, because of how massive the galaxy is. And to be Honest if we are gonna throw Chaos a bone, might as well throw the Imperium one, maybe get a Primarch back.
I honestly don't care if they advance it or not, I am more on the side of fixing current fluff(Get away from my Crons Ward), getting rid of Retcons that shouldn't have occured and minor tweaks for fixing contradictions. I like 40k as it is. A big stalemate.