The grapple is a difficult topic. I'll make a few comments that I know will be true... I can't give specifics because I won't know more than this until we impliment something and see how it works.
1) The WFA grapple sling will not be in WFR. That sling was the result of a prediction bug and it is something I fixed way back in 2.1 but popular opinion was such that it was too late in the game's lifetime to make such a huge change.
2) The grapple in general will not be the primary method of movement for grapple classes. In WFA classes with grapples used it on the floor to move faster... that is something that needs to be fixed to make non-grapple classes more equal in terms of movement speed. The grapple will not be overly slow but it won't be the primary method of locomotion. It will most likely be effected by gravity and will wrap around objects if the player's movements cause it to do so. This will allow some trick grapplers to move in non-linear ways by wrapping their grapple around objects as they swing past to radically alter their direction of travel.