Not to moan prematurely before it all goes live and whatnot, but i only just got off having an awesome amount of fun on the PTR as destro and this change means 20% less damage on chaos bolt (emberstorm + CoE). Depending on how the mechanic works of these two stacking it may not be a straight up 20%, but whatever. Kind of hope the damage gets tweaked back up to compensate, i know they said they're reviewing damage all the time, so i hope that the intention was for the damage to be around how it was with those two and not without.
On the plus side, i guess no-one's got any real resistances to chaos damage apart from those with a blanket magic resistance (i assume chaos still falls into the magic school). Also, the whole instant soul fire thing is awesomely fun, hope they don't change that.
For those who haven't tried destro yet, it actually seems totally grind-viable now, my mana regen is sweet and my hp is always being topped up with the DS-like health regen on fel armour, had no down time at all on 68-70 mobs around Black Temple. Mobs also die insanely fast on an immolate > CoE > Shadowfury > Chaos Bolt > Incinerate > Conflag > Shadowburn rotation.