Limiting your idea so that it may one day be possible:
Needs a high, 1 use per 2-3 fights cd. Needs to become unusable/break on combat. Should have a modest stamina/resource cost to make sure that if it is used to further escape a combat sitation, the player does not use it without consideration.
However, I think that balancing too much pvp around terrain fighting leaves some of the slower melee classes out of luck. Have you ever tried to melee a dragoon who didn't want you to in world pvp? Same thing here with WaterWalkEscape, Backflip, and eventally, once distance and resources are up, Smoke. I do not see ninja's having any trouble closing gaps when played competently with the current skills.
Another tiny objection is that I want to see increased use of vehicles (boats n carts) for HC rather than all this warping/easy sprint mode skills people want, but that is a personal note.
This all being said, if implemented my spec would love anyone else to have this, one arrow while you're in Jesus waterwalk mode and you either fall into the water (gg ranger) or can be ice'd until you do.