As destruction you will be hard casting soul fire, which is your main ember dump. It has a 4 second cast time, and the only thing that will reduce the cast time beyond haste is Destructive Influence. I consider DI to be terrible spell design, because it causes us to rely on a pet. First of all, we were told that all pets would be equal in MoP and we would be able to choose based on utility and personal preference. With Glyph of Demon Training, the only viable pet will be the Imp, since that glyph reduces the cast time of Firebolt. The next issue, is that I really want to be able to use Grimoir of Sacrifice, but having DI essentially prevents me from doing so.
DI also doesn't fix the issue that arises once you take the second purpose of Soul Fire into consideration; to have a mana free spell with a long cast time that allows you to regen mana. You would have one very fast Soul Fire, and then you would have to cast another slow one to regen mana.
I personally believe that Soul Fire should have a 2 second base cast time. Then you remove Destructive Influence because it is no longer required. Two 2 second Soul Fires sounds a heck of a lot better to me than one instant Soul Fire and one 4 second Soul Fire. In order to not break Demo, Decimation would have to be changed to only increase the Soul Fire cast time if used on targets above 25%, while not reducing the cast time anymore.
In case y'all are wondering why I'm seeing the current state of Destro in Beta as an issue. A couple of weeks ago we got a blue post that outlined some of the Destro changes they had planned for Destro. Many people that actually looked into the theorycrafting and what these changes would mean, didn't like what they heard at all, because it had some really stupid implications. It is simply disconcerting to me to see these changes still in game, since it shows that Blizz obviously likes this design.
Also keep in mind that I'm not simply complaining, but am expressing my concerns about a very valid issue. I love my Warlock and I want to continue playing Destro in MoP, but some of the current design decisions are simply not fun or engaging.
Thoughts, comments? Personally I cannot stand the thought of 4 sec casts in my rotation. My question to you guys is this. Do you see yourself enjoying a spec that hard casts a spell for 4 seconds?