This is going to sound petty, but the more I see people play TS in 9th, and the more I play 9th, it's starting to feel like very few playtesters (if any) really concentrated on Thousand Sons.
The Psychic phase has been turned down just from the baseline rules changes (Command Re-roll, Detachment Rules, can't cast after fall back, protecting characters, etc).
Conversely, armies with very good troops and a low requirement on support entities like HQ's, look really good. Astra, AdMech, Custodes, (so far) look good, and play well.
Armies hit by my personal qualifiers include: Grey Knights, Thousand Sons, Eldar, etc. (those top heavy armies which are especially hit if siding with a heavy psychic design element)
I don't think Chaos Space Marines are much better off because of their similarities in list design, however they do have some decent mid range shooty choices which I still think Thousand Sons are greatly reduced in. (The Psychic phase has historically been our shooting phase). Add on top of this we have lost our ability to Smite at WC5 with our mono faction.
So where are our apparent strengths for 9th? Bodies of decent infantry. Powerful Psykers (If left unchecked). But oddly we have to be careful about Close Combat if we look at our historically 'strong' builds. Let's remember not too long ago -every- half decent "Thousand Sons" army list seemed to revolve around Ahriman + 2 Psykers in a Supreme Command, and then put a functional army / faction in the other 1600 points you have left over.
If the troops are where it's at for Thousand Sons, I almost think we have to adopt our HQ's to pure close combat. That sounds crazy, but retreating from Close Combat (falling back) is death for us.... I've tried it.
Here's the conundrum: you want to stay in CC to start casting. However, by doing so you are almost certain to get peeled apart by Astartes, Custodes, Nids... fill in the close combat nightmare of your meta. No one in their right mind would argue our infantry is close combat capable, except perhaps... Goats (ugh).
Bear with me here, but what I'm suggesting is we might be entering an edition where we have to be able to keep SoT, Rubrics, Goats in CC, and keep a real 'wrecking ball' HQ in there with them. Trust me, I've felt it first hand, we can't push back strong, or elite CC infantry without it. BUT if you're hitting back like a truck with Daemon Princes, and an Exalted Sorc with Seer's Bane, and/or loading up on Diabolic Strength more often.... Daemonic Talons, perhaps the Tzeentch sword that removes invluns? (Can we take that in Thousand Sons?... I know I did, but not sure if it was legal.)
Anyway, that's my overall assessment. Last edition my HQ's were more or less paper, but it didn't matter. I think this edition the whole army has to be engaged... not only to keep your HQ's untarget-able but also help push back with heavy counter attacks, because we aren't out shooting/ Pskyering anyone to death. The psychics have turned to utility and damage. It's a game of board control now.
(P.S. What I would do for psychically capable Dreadnoughts in this edition!)
Yeah, I'm thinking we are going to be relying a lot more on the likes of hellbrutes and contemptors just for the close combat punch and more damage two.
It's the fact we don't really have that much shooting that is more then damage one that is a main issue for us.
The risk with the beat stick HQ's is the defender choosing stuff first, we will have to be careful about that.