I'd love to see different buffs/auras/spell disciplines for the different sects.
I was hoping this would happen in the move to 8th ed, but it didn't, and the 9 "new" Cults listed in the 8th Ed Codex are all too predictable and distinctly uninspiring (Cult of Magic? Cult of Change?).
It's a very long shot, but I'd like them to have put some effort into updating the TSons and bringing back Corvidae, Rehati et al, and give them some more flavour/unit options.
It surely wouldn't be too much effort, if Prospero is now churning out munitions, to release a Rubrics arm-sprue with plasma guns, etc... Soulreaper cannons for everyone, double flamers, just something to combat NuMarines!
This might just be me, but I see it more in mutated machinations.... spawn with mutations, melded with death crawlers. More realistically we get use of Venom Crawlers etc.
I can handle that though. What's always torn me between my Black Legion and Thousand Sons is I don't really like a lot of the Daemonic Engines we have, where as the chaos ones are newer, and sometimes a little more functional (Master of Possession helps a lot.)
Hypothetical: Let's say we take that storyline from the Baal book and look at Magnus' war factories. Let's say that opens up new or recycled Daemonic Engines for Thousand Sons. Maybe one of them is a psychic Dread. The model exists, it would simply have a special psychic ability and we'd actually have a character Dreadnought. To me this is all good stuff that helps sell existing models.
Now taking that line of thinking to the next level.... what if we get a partial Eldar Treatment: IE: Let's say.... any psyker that has smite (all of course) can replace smite with a modified version of all of the Master of Possession powers?
So we could get rid of baby smite on our Troops/Termies/HQ's (if we want) and start getting powers that... Increase invuln in an aura of Daemonic Engines. Or let you reroll the abilities of Spawn, etc, etc.
I could totally get on board with that. I'd love it.
I'm sure I'm over thinking it but I think this is the sort of stuff they could easily do because 1) It already exists, and 2) no new sculpts required!