Well, since everybody is going to have the feature, it may / may not ruin the pvp experience.
I, personally, do not know much about the 1.7 update, but just because it'll be fair does not mean it won't ruin the pvp experience. With BSM, players who get knocked back with arrows can instantly sprint forward again and basically don't take knockback - using arrows to attack players while they're getting knocked back (a good tactic) will be ineffective; using a fishing rod to do the same thing will be ineffective. Furthermore, running away across terrain will require no maneuvering - if you were to clip a block in a chase scenario with someone not far behind you, you'd die, but BSM can easily change this completely as you can sprint almost straight away after clipping it. When cutting people off, you're sprint will not die and it'll be a lot easier to cut people off - once they get a hit, they'll be sure to finish them or get a few more. Those super long chases that go on forever will be more common - BSM allows players to run forever without their sprint ever breaking. The simple charge in pvp will be quiet interesting though; seeing two hackers run straight into each other is pretty funny and I'm curious to see what it would be like on a regular basis. All in all though, you can clearly tell that BSM will change the pvp experience.
Take note: I'm not familiar with the 1.7 update, but these are just some of the ways that BSM itself does affect pvp - I'm not sure how Mojang will be implementing their 'BSM' and how it will work in comparison with the current better sprint mod.
