Ok, so we've had a lot of threads, on various forums, from Shadow Priests and Affliction Warlocks about this subject. We've had some other specs / classes which use DoTs comment about how it's bad that DoTs don't scale with Haste. So far I've yet to see a single serious poster actually disagree with or like the fact that DoTs don't scale with Haste. I also haven't seen a solution offered up that hasn't been shot down. So here's a solution I've done a bit of thinking about over the past couple of weeks. It has a few problems, that I'll get into later on, but I really think this concept could go somewhere, and I'd like to get thoughts and opinions from others in the community.
Currently, if a DoT is applied, it will deal steady damage in a steady interval. This damage scales with either Spell Power or Attack Power, and in a few cases these DoTs can crit. Haste, however, has 0 effect on the rate at which an individual DoT does damage, and has some marginal effect on the speed at which specs with multiple DoTs can apply them.
One solution that has been offered up has been to allow the entire attack, to scale with Haste. If a 15 second DoT deals damage 5 times in 15 seconds, let 10% haste lead to this spell dealing damage 5 times in 13.5 seconds. This solution is usually rejected due to fears that the specs which would be affected by the change the most would wind up with completely unmanageable rotations, especially when variable duration Haste buffs such as Heroism and Trinket Procs are brought into play.
A second common solution is to allow just the duration of the interval between DoT ticks to increase. This leads to the problem of what to do with the extra time at the end of what would normally be final tick of damage. The common solution to this additional problem is to allow an extra tick of damage if the player has enough haste rating. Shadow Priests in particular do not like this solution, as we would prefer smooth scaling with Haste where each point of Haste Rating is actually beneficial, as opposed to this system where we only notice benefits DPS wise in particular chunks of Haste Rating. Note, this system (with or without the extra ticks) leads to increased damage, but without the extra ticks is functionally the same as the first proposed system
So then, I started thinking about how could we prevent over-complication of the overall rotations of DoT-based DPS specs, without overly increasing our DPS output. I also wanted to make sure the actual scaling happened in a "smooth" manner.
The first step, in my opinion, is decoupling the resets of both the duration of the DoT debuff and the interval of time between ticks that occurs when a DoT is reapplied. Currently, the final tick of damage on a DoT occurs at the end of the DoTs duration. We currently aim to reapply DoTs right at the end of this duration, to avoid "clipping" of that final tick. If we clip this final tick of damage, we wind up extending the duration between DoT ticks, resulting is DPS and raw damage losses that are significant over the duration of a boss fight.
This issue is manageable at the moment, becuase DoT durations remain constant. Through practice, we gain a feel for when a DoT is going expire and when it should be reapplied. If we start to have to consider that the final tick of damage will occur at a variable interval, and if this interval can actually change randomly during the fight, we wind up completely reliant upon addons to manage this timing issue, as it would simply be too complicated for the average player to keep track of on their own. I know for certain that I couldn't keep this kind of exact precision, and I used to play percussion in the high-school marching band (1, 2, 3 4, 1, 2, 3, 4 running through my head for hours at a time)
Let me describe what I'm proposing here. We will use Super DoT X1000, which lasts 15 seconds, and deals 1000 damager per tick in intervals of 3 seconds. With 0% haste, over the course of 1 minute it will be applied 4 times, ticking 20 times, dealing a total of 20,000 damage. The spell with have 333.33 DPS. At 10% haste, with the spell being reapplied just before the 15 second mark wears off, we still have only 4 casts of the spell but we now have 22 total ticks of damage, resulting in 22000 damage. We're now up to 366.67 DPS, and have about a 10% increase in DoT damage. This is a noticable increase over the course of long fights, as well as in brief fights that might only last 15 seconds.
Now, what happens if a DoT is reapplied after the debuff wears off? In this case, the most recent application of a DoT is treated as if it were the very first application of the attack. At higher haste ratings, a late recast of a spell will result in lower DPS. Thus the skill set currently employed by DoT classes is maintained, we're just applying DoTs slightly earlier than we were before.
One question that has been asked of me, is if this system would make early application of DoTs a way to DPS poorly (or in a lazy manner) but still pump out good DPS. First, I would argue that if you're not reapplying DoTs at the optimum time, you're missing out on some other spell that would have dealt more damage than resetting the timer of the DoT debuff does. Second, as you begin reapplying these DoTs too early, you actually start to loose mana efficiency.
Let's look at Super DoT X1000 again, this time giving it a mana cost of 800 mana per application. Using the 10% haste model, we're going to have DPSer A apply the spell at the right moment, while DPSer B applies the spell every 12 seconds. Both players do the same amount of DPS, 366.67 with this one spell. DPSer A only spends 3200 mana however, resulting in 6.875 damager per man. DPSer B has cast the spell 5 times now, with a total mana cost of 4000 and only 5.5 DPM. DPSer B is consuming mana much faster, getting lower efficiency from his casts, and is using a play style that risks him running Out of mana later on in the fight.
There are two problems with this model however.
1) Single Target Mana Efficiency increases with extra haste. The traditional counter balance to the large DPS increase Direct Damage casters get from Haste is the fact that they run through their mana pool at a much faster rate. However, with "perfect" play, where DoTs are refreshed shortly before they would naturally fall off a target, we actually see DPM increase. Let's look at SDx1k with 0% haste again.
We're doing 20k damage in 60 seconds with this spell, resulting in 6.25 DPM. Remember that at 10% haste with perfect play, we had 6.875 DPM. With sloppy play though, we only had 5.5 DPM. So, do we leave this as is? It seems right that the player who spends much more time perfecting a rotation would get rewarded for it, but I'm not sure if Haste should actually increase mana efficiency.
Alternatively, we could look at increasing mana costs of these spells, so there is a very significant risk of running OOM if you don't play perfectly, but good play results in
2) Multi-DoTing becomes more powerful at certain intervals of Haste. Ok, so we know that a DoT falls of a target with only short-term DPS increases if it's not reapplied. Keep in mind though, that this model allows for extra "free" ticks of damage at certain intervals of Haste. At 20% Haste, SDx1k for instance, would tick 6 times within a 15 second window. At 40% Haste, we'd get a seventh tick. This is obviously a large DPS increase in single target situations, but at those levels of haste you'd expect something like that.
Now imagine the damage output of these spells with those levels of haste, and 5 targets I could apply the spell to. While I've got DoTs scaling wonderfully in single target situations, they now risk becoming far too strong in situations where I can multi-DoT.
My solution here is to borrow from the design concept of AOE attacks. Attacks that deal damage to many targets at once deal reduced amounts of damage if you have too many targets selected. I propose that DoTs begin to deal less damage if they're on too many targets. There are a couple of ways this could be done, but I would suggest that DoTs which can exist on multiple targets should suffer some significant loss in damage output when they appear on more than X number of targets. Super DoT x1000, for instance could suffer a 20% penalty for each target after the first target that is is applied to. It would deal 100% damage to target 1, 80% damage to target 2, 60% damage to target 3, 40% to target 4, and maybe 20% damage to all remaining targets, until some of the previous ones begin to die.
If you're not careful, you'll wind up with a situation where most of your targets are in the 80% - 40% of max damage range. This discourages a lazy play style of simply Tab - DoTing our way to victory, as at some point we become ineffective if we don't go back to single target DPS attacks. It would also provide a steep counter-balance to how well DoTs scale with Haste when they're just on a target for a single debuff duration.