I see some big problems with this ability, it is incredibly underpowered. Granted we don't know much about it yet, but anyway you look at it, its not that great.
Assuming it just gives you the ability to cast while running...
-long cd, short duration, very situational.
-can still be snared (crip poision we cant dispel anymore)
-can still be interupted
One of the easiest counters to this ability is another shaman lol!! Wind Shear would make this feel very useless, also charge, death grip ect. The fact that your casting leaves you open to lockouts from too many sources.
Now....lets say they give you 10 sec of freedom and you can't be interupted as well.
Then why do we even have to cast in the first place? Why not just trigger 3 instant casts, like 3 nature swiftness, but for any element, but give it like a 2 sec gcd between each cast. By saying we can cast, they want a very easy counter thru interupts or stuns ect.
Sounds cool on paper but not all that great when you think about it in practice. I know Blizz has the right intentions and is trying to give us some tools for mobility, but this probably isn't the way to do it.