[Mage] Arcane Blast update

As somebody who would really like to raid as arcane I'd like to see arcane blast be a viable nuke.

It has to do higher damage than 18pt talented fireball/frostbolt.

It was mentioned at blizzcon that arcane would have mobility, but playing as arcane and being tied to having to start your cast time nuke as soon as you fire off your arcane barrage gives you a 1.5s window of mobility.

I'd like to see something like a modifcation of the old AB mechanics having 3 stacks scale to instant cast 2.5->1.75->instant, and having the debuff be long enough so it doesnt fall off between arcane barrages but does during MBarr procs.

Itd be an interesting mechanic to ramp up damage and increase mobility in PVE.

having to stack the debuff before its instant cast would keep its use in pvp scaled