We actually tested this option of a dedicated movement skill a couple years ago. We decided that having your movement skill as part of your build and the decision of if you should have one or not was a good thing to have in the game.
As for the initial suggestion of 2 more skill bar slots, 1.0 will not have it. Post launch, it would take a pretty big shift internally to cause it to happen. We really like the 5 skill limit a lot.