As stated in the Blue post for the Legion Pvp preview, gear will not play a factor in pvp in Legion, however the honor talent system will take its place. For instance instead of seeing "lfm rbg's 710+ Ilvl and 1800 exp req.", we will be seeing "lfm rbg's level 50 honor and 1800 exp rbg's.", (just an example, the numbers aren't specific but you get the idea).
Right now to my knowledge there isn't a specific amount of time it will take to get from level 1-50 honor rank, however it probably won't be a quick feat. (just an educated guess) Once you hit honor rank 50 you'll have unlocked every talent option for your spec and that is how you will have an upper hand on people in pvp (other than skill, gear will have little impact)
So with the main goal of end game pvp going to be you having level 50 honor rank, will prestiging be even feasible for the end game pvper? Why would we want to prestige if it means resetting every talent and having to grind through it again? Nobody is going to want a rank 1 honor person in thier rbg or arena group, and if you want to prestige you have to reset your talents and you lose all your moves you've unlocked.
I just don't see how this is going to work. You want to prestige to get better rewards, but can't because you have rbg's on Tuesday and it is Sunday and it takes a week to go from 1-50 (just an example, as stated there isn't a set a out of time it will take to get from 1-50)