Without MWC, should I wait demon soul cd to cast meta?
Or just simple spam meta?

Demon soul doesn't actually buff Meta in the same way that MWC did. With MWC you had to have MWC active before casting meta because of the snapshot nature of mastery. If you are no longer using MWC there isn't such a requirement anymore.

To answer your question more specifically, Metamorphosis lasts 30+6 seconds. Demon Soul will last 20 seconds because you are using it with the puppy which increases periodic shadow damage. Since the trinkets you are likely using are CotC and WoU you will not need to align those trinkets either. This means it would be optimal to have demon soul up within 16 seconds of casting Meta or at least have demon soul and meta up long enough together to get a recast of bane of doom and maybe a corruption in. What is more difficult might be aligning the other cool downs together like Blood Fury, lifeblood, engineering trinkets and things of that nature with Meta.

Optimally if it is possible you would want all non-snapshot cool downs to be used in a such a manner where their full duration can be spent under the effects of meta.

Should you wait a few seconds to pop Meta to align cooldowns? The current BiS Demo set up does not delay casting Metamorphosis for anything.

This isn't an issue with the Opening Meta + pet swap but those Meta casts thereafter.

OP says that 0/31/10 is used for multi-target fights, but I have a question:
The difference between 3/31/7 and 0/31/10 immolate's cast time is 0.3 seconds before haste, but Corruption's damage for 3/31/7 is ~12% higher (and it's part of multi-doting). I can not simulate multi-target fights and I'd like to see the difference between them in dps.

A couple questions about the normal BiS list:

1. Isn't Tentacular Belt better than the one you listed? Even though we loose 20 int from the blue socket, having mastery on the item outweights that?

2. Isn't Kavan's Forsaken Treads also better than the one you listed? Again, even though we loose 20 int the yellow socket, having hit on them item compensates that lose?

I simmed those on my character and both simmed higher, but as chardev isn't updated for 4.3, and I didn't check for full 397 gear, even though I reckon those will still sim higher, and they are also easier to obtain.

In regards to the 1574 Immolate threshold, the significance of this is far greater in fights with more than a single target (just about every fight this tier). In a single target fight you are correct in thinking that it shouldn't have an effect, but there was a decent increase in DPS when I reached this threshold in simcraft. Where the relationship is between them is something I am still trying to figure out.

Last time I tested it, Holy Radiance did not proc DI, this may have changed since then. I will test it again.

Not likely. The increase received from Demon Soul: Felhunter is minimal overall and you probably wouldn't want to wait more than about 10 seconds. In most cases, especially before heroic BiS, Demon Soul should be up before meta ends anyway.

As a side note. BiS Lists are up and Epic Gems have been included in the thread. A trinket overview should be coming soon once I get the time. At the same time I have been doing a lot of simulations to try and find a true relationship between Demo and Haste, especially where thresholds are concerned, but so far the results are somewhat inconclusive. For not the stat priorities should be correct for 9/10 situations.

Just a quick word on the haste plateaus.
Seeing as there is a fairly large amount of haste on the current gear, it is for a lot of setups in the "mid-range" (378-379) quite unfeasible to actually get down to 1573 haste rating.
As an example, I am in the rather odd situation of not having any crit rating on my gear at all - thus I would have to reforge something like 600 haste rating > crit rating to actually get down there, which would be detrimental to my DPS, given the current scale weights, even on single target fights. (And well, seeing as there is only one entirely pure single target fight in Dragonsoul HC, the point is almost moot)
Just remember, they are only guidelines, and are not written in stone, so take them as such, was my point.

I've just been doing alittle bit of playing around with my warlock, especialy with the thought of no longer using MWC as gear levels increase and the trinkets WoU and CoC become the way to go.

with this in mind, ive come up with the concept of trinket swapping MWC (hear me out). i know its been hotfixed to no longer provide mastery once unequiped to counter the earlier exploit that was running rampart. this made it a waste for everyone HOWEVER we as demo locks get the lovely feature that our meta SNAPSHOTS our mastery! so we dont care if the buff falls off as long as we have it snapped already.

Just for the sake of testing its potential i have been giving it a go and feel im getting it to work with great results.

What im doing is on the countdown to pull, poping the trinket with my prepot, then hiting meta and a trinket switch macro right on the zero (note the trinket im switching in is WoU as it has no ICD to trigger making it the perfect candidate). this should theoreticly boost the first meta for a good 20% thanks to mastery while still allowing the rest of the fight to go as planed.

I am delibertaly not popping doomguard till the actual rotaion begins as i figure the sp from procs in the first 5-10 sec would be more benifit than just the mastery of MWC. (might be wrong here, would be interesting)

Now is there a way someone could actually sim it (as i lack the skill to) to make sure this would give the benifit i think it should.

I want to first thank for this amazing thread, it helped me alot to improve my performance in raids.
I got two questions regarding gearing
Ti'tahk, the Steps of Time or Volcanospike HC + Molten Scream HC ?
Will of Unbinding + Moonwell Chalice or Will of Unbinding + Cunning of the Cruel Raid Finder (i know normal one it's better) ?

I would advise against Will of Unbinding, because in practice (aoe fights) it is worst trinket for demo, it dosnt proc from 3 of our main aoe attacks (felstorm, hellfire, immolation aura) and is guaranteed to drop in any aoe situation if you follow your regular aoe rotation. You could make one more timer to watch in order to cast something like corruption so you can keep stacks in aoe fight, but that is more hassle than it is gain.

Immo aura is passive. It's easy enough to stagger your HoG and Shadowflame out a bit, dropping a Corruption for improved MC uptime or even a Felfire on the main target and recasting HF ahead of time . Most AoE packs go down fast enough that the idea of ignoring 900 int for most of the fight is a bad bad idea.

I did some trinket analysis using my spec: Scathbais @ Mal'Ganis - Game - World of Warcraft
Note that I have the 4-pc t-12 and 384 LFR tier legs (damn Vanq tokens drop all the time for us).

Out of the three DS trinkets (WoU, IOTCM, CotC) only the LFR IOTCM does not replace MWC as your second trinket. All three LFR versions provide enough DPS to replace DMC:V assuming you keep MWC as your other trinket.
Assuming we equip at minimum WoU from LFR, every trinket except IOTCM LFR would provide better dps than keeping MWC and pet swapping. In my simcraft, all I did was get rid of the pet swapping action and all pet swapping related actions for simulations that did not use MWC.

Note, I just realized that I did NOT simulate pet swapping without MWC. I will post those results next.

Here are my results:

Normal DS gear:
41237 Scathbais current gear (trinket 1 = DMC:V and trinket 2 = MWC)
42013 trinket1=will_of_unbinding, ilvl=403,trinket 2 = MWC
42168 trinket1=cunning_of_the_cruel, ilvl=397,trinket 2 = MWC
41979 trinket1=insignia_of_the_corrupted_mind, ilvl=397,trinket 2 = MWC

42013 trinket 1 = WoU, trinket 2 = MWC
42737 trinket 1 = WoU,trinket2=cunning_of_the_cruel,ilvl=397
42212 trinket 1 = WoU,trinket2=insignia_of_the_corrupted_mind,ilvl=397


LFR DS gear:
41237 Scathbais current gear (DMC:V and MWC)
41649 trinket1=will_of_unbinding,ilevel=390,trinket 2 = MWC
41858 trinket1=cunning_of_the_cruel,ilevel=384,trinket 2 = MWC
41817 trinket1=insignia_of_the_corrupted_mind,ilevel=384,trinket 2 = MWC

41649 trinket 1 = WoU, trinke 2 = MWC
42336 trinket 1 = WoU, trinket2=cunning_of_the_cruel,ilevel=397
41609 trinket 1 = WoU, trinket2=insignia_of_the_corrupted_mind,ilevel=397