Actually madness spec will probably have the most to gain from the adrenal/stim changes than any other class spec. We have very little burst, but we do have great constant dps. Therefore, with the longer duration, I would not be surprised if we see an increase in dps as a result of this change. With a 31 madness sorc, you would gain benefit to Crushing Darkness, Affliction, Creeping Terror, and Force Lightning all at the same time with little to no drop from cast time; not to mention the increase to Death Field. However, your more traditional burst classes will have one or two abilities affected with little to no damage occurring during their cast time. So they may gain 1-2k in that time while we gain 3-4k because of the constant damage occurring. (Numbers are purely hypothetical)
This, of course, will be entirely reliant on the actual difference in numbers, but I think this should not be viewed as a nerf to madness sorcs until we see the actual changes.