I agree with bara on the HQs...

HQ wise (current codex) I have only ever faced company command squads (melta chimera only variance occasionally in a skimmer)..
Never faced a Techpriest (where as master of the forge is darn sexy as an HQ)
Priests (whilst chaplins took a bit of a hit with the whole down to int 4, they still have a roll not seen priests even though they are given free reign)

Primaris psyker (when other codexs librarians are awesome their HQ sucks and Is outdone by their own panzering elite version)

I faced one lord commisar in 70-80 games against guard but that was on the bottom tables at the GT and I was helping the bloke play.
Yarrick?Deddog? I've played against creed a couple of times but never kell.

Because of the troops structure one unit of many components I'll be generous and treat Al'rahem as another HQ option I've faced 3 ish times.

In the whole rest of the codex FOC slots there are only 3 things not able to be super awesome incredible.I wonder if GW design "balance" with a this will be their weak FOC bit (chaos fast attack, grey knights fast attack, a few others have weak elites,Smurfs is troops etc)

Smurfs is an odd example though.. the whole unlocking a whole different tactical approach by changing one model out is very much what people tell me is the good bit about warmahordes..I have 30 tactical marines.. suddenly they are all really fast, suddenly they are all really killy (shooty, lysander or vulkan, close combat chaplin), suddenly they are all better than fearless, suddenly they be invulnerable (libby) suddenly they are all sneaky outflankers, suddenly they can ride on bikes (only last one requires actual model change)

Here's some more chaos rumors from Bell of Lost Souls;

http://www.belloflostsouls.net/2011/11/ ... bbles.html

That bols stuff is culled from ghost on 'seer.
The dude has started a (excellently complete, I think) summary of this stuff here http://www.warseer.com/forums/showthread.php?t=324882

He also compares differences with other "whistleblowers", rather jolly.

Both of those abridged summaries miss the bit where ghost talks about plastic plaguebearers in the 6th ed launch boxset (he then teases when asked if that means moar demons by saying.."maybe its just that the scenario between two other armies is set on a demon world")
I don't know if that means you take him with more salt or suddenly hold off on buying plaguebearers..I'm going to carry on building my rat plaguebearers.