I plan on playing the Daemons in the coming months as I finish painting them up. I have a few more orks to paint up to allow my nob biker army to be fully customizable, but the Daemons are going to quickly get their paint on. I have some thoughts of them, and I think I might have an ok army that would do well in the new environment of 5th edition.
Before I go into that, I think controlling and planning your assaults will be so important in the coming edition. You are going to want to kill enough in the first round, to ensure the hit back won't be bad, and hope they stick around so you can kill them during their assault phase, so you can move more and get to another account. Also, I think splitting assaults will be a big thing, and one of the ways to abuse the sheer assault power of the daemon force.
Onto the list as I am thinking of it with explanations for each unit.
HQ: The Masque - She will be attached to the Daemonette squad and will give me a way to affect multiple units, and hopefully help keep my daemons coming out on top in the assault phase. Since she is one half of the HQ choice, my other herald is
HQ: Skulltaker on a juggernaut - He is my big baddy to take out MC's, Nobs, and other nasty units. His auto killing ability will be great vs any multi wound creatures, and he is one of the few guys that the Rending Nerf isn't nearly as killer as it is for the others. He is attached to a Bloodletters squad.
Troops: 19 Daemonettes - Icon of Chaos : Flesh bags for the Masque to be protected. A nasty unit in HtH versus marines and smaller, elite assault squads (ie not orks). Good for putting 5+ wounds on something. With the Masque and their running around ability with Pavanne, a nice support style unit. Also good for a counter assault
Troops: 19 Bloodletters - Icon of Chaos : The meat with Skulltaker. A scary assault unit and a threat that will have to be dealt with.
Troops: 20 Plaguebearers - Icon of Chaos : The scoring unit, tie up unit, maybe a shooting magnet. One of the units I want down first, since most likely the icon will survive for awhile.
Elites: 5 Flamers of Tzeentch - Bolt of Tzeentch : My elite Jump troop that will be annoying and bring some paint to troops in cover. I want them to hit in the back, and then jump out and around, causing some annoyances. The 4+ inv save might also make them really annoying to deal with.
Heavy: Daemon Prince, Mark of Tzeentch, Iron Hide, Master of Sorcery, Daemonic Gaze, Breath of Chaos X3 - Really expensive, but very annoying and hard to deal with. I want them to hit down, cause some scary thoughts and make my opponents play incorrectly. There will be games where they just live way to long and bring down too many tanks/hard to kill creatures. The shooting will come in handy, since they can flame the squad and then shoot them with 3 str 5 ap 3 shots.
I am not sure about this list, as it will most likely change as I play it, but it might be a fun starting off point. I think the Daemons have some potential, they just need a lot more work to get them playable.