Let's see about that maelstrom weapon:
Let's assume two 2.6s Weapons, 25% haste from Flurry (~84% uptime or something, should be fine), 20% from Windfury Totem and 5% from static haste. So we get (rounded) an average weapon speed of 1.6s.
Now how many attacks do we do in 15s (yellow hit cap, 10% miss for white), let's assume 3 wf procs and 3.75 stormstrike swings, no dodge or other fancies here
0.9*(15/0.8) + 2*3+3.75 = 26.625, rounded to 26 for now, let's make it easy and we'll take 25 for now
So we have 25 swings in 15s on average
That maelstrom thingie is a bernoulli experiment with P(x>=5):
P(x>=5) = 1- P(x=0) - P(x=1) - P(x=2) - P(x=3) - P(x=4);
So for 25 swings and 35% crit (fits with the 84% flurry uptime) P(x>=5) is 0.96, we can pretty much safely count on maelstrom weapon to give us an instant lava burst every 15s.
Now let's do the same for 10s, since we basically want it every 10s, since elemental devastation is only 10s long.
So let's assume 18 swings in 10s, maelstrom Weapons uptime is now 0.81.
So for the 10s case, we can say that together with the probability of critical shocks and (maybe lightning shield?) we can safely assume we will have an elemental devastation uptime of > 80%. Which should be fairly nice.
We certainly could need addon help there to tell us when 5 stacks of maelstrom weapons are up to prevent accidental swing interruptions from casting attempts, if they actually implement that a 5 stack maelstrom is an instant cast without swing timer reset. If not, forget everything above
