I'd like to see;
-
NO MORE GOD DAMN ROLLING FOR WAVES!!! (seriously, what was Alessio smoking when he thought that one up?!)
- Psychic abilities and some freaking psychic defense please!
- 'Better' deep strike ala desent of angels or something similar
- pts drops across the board
- 'Warp Gates' as a character upgrade that work similar to webway portals
HQ:
- Exalted Daemon.
An
IC on the level of a space marine captain in terms of stats, with options in a similar vien to a daemon prince. (ie: marks, a smattering of gifts, psychic abilities)
- Heralds to give a bonus to their relevent daemonic core unit. (ie:
HoK gives Bloodletters 'Prefered Enemy: Everyone!)
Elites:
- Plagueriders of Nurgle.
Plaguebearers who ride beasts of nurgle. A non-slow & purposeful nurgle unit, but not proper cavalry either! (they're still nurgle slow afterall)
- Changebringers of Tzeentch.
Flamers riding discs of tzeentch. More shooting abilities to choose from perhaps, and a killer invuln save, but rubbish combat stats. Basically the 'scary' shooting unit that's not a daemon engine.
Troops:
-Put the Furries here and make them not suck please. (right now they're litterly the zombies of
40k 
!)
Fast Attack:
- Pleasureseekers of Slaanesh.
daemonettes riding fiends. New 'super cav' that are basically glass cannons. Lots of high initiative attacks, but don't let them take hits too well.
- Chariot of the Gods.
No more 'herald only' option, basically a 'unit champ' like an Alluress or Bloodhowler who can take a gift or two and an Icon. Perhaps have them come as units of 1-3 as well?!?
Heavy Support:
- DAEMON ENGINES!!! (seriously, what gives
GW? Give us damn daemonic forges and make them customisable ala battlewagons!)
Of corse, I have a sinking feeling that we're at least a year or two off of seeing any love at all, because Daemons are still one of the top armies in fantasy, and
GW will likely want to do a double release with us since we can play across both systems.